Hello and welcome to my unit guide. This is the first part of it - covering infantry. Expect later to see, Cavalry and Artillery unit guide as well down below. There may be also a lot of changes in this post to reflect correcting mistakes, a little bit more going into detail etc.
Ok, embrace for a lot of unncessary text. This is also according to my opinion - and in general so in some case you may want to switch things up. I hope it will increase your personal Army Tradition 
(Disclaimer - if you're already at 100 Army Tradition, it will not help you )
UPDATE: Guide now also has a pdf version of it. It's attached to this post, or alternatively you can download it from my dropbox, by clicking it HERE
I will start with infantry in this post: (next tech groups will omit the tech modifers analysis)
INFANTRY
Tech 0-4: Latin Medieval Infantry. Halberd Infantry damage increase from +1 Shock is up to (if the Wiki Casaulty formula is true) 5 men per regiment in shock phase (assuming 1000 men survived to the shock phase in regiment, otherwise it is unit %*5). Also on tech 4, you get military tactics which means that bonus is just 3,75 per regiment in shock phase. And in most cases the morale is clear winner on the battlefield early on, so it's best to invest in a unit, that can help at least mitigate some morale damage (which especially with tech 4 and increased morale (=more morale damage) can be day saver. You may hovewer stick with Halberd Infantry for tech 0-3* if you really find the damage increase that important, but beacuse you may be during war when tech 4 hits, switching unit types during war can be nasty, so it may be better to stick with Latin Infantry.
* - standard game starts with tech 3.
Modifiers for tech 0-4:
- 0.25 at tech 0, 0.35 at tech 1-4. Fire phase is neglibile at this point, units do not have any fire pips, and any +fire pips come just from the leaders.
-0.2 at tech 0, 0.3 at tech 1 and 0.5 at tech 2-4. Shock phase is much more important at this point, infantry will deal more damage at this point.
- 0.5 at tech 0-3, 0.75 at tech 4. Tactics of 0.5 means that 100% discipline units will deal 200% damage (so in reality damage modifier is twice as high, as it would indicate from the damage modifier for that phase). Tactics of 0.75 means that damage coming from modifier will be 1.33 times higher.
- 15 at tech 0-1, 20 at tech 2-4.
- 2.0 at tech 0-2, 2.5 at tech 3, 3.0 at tech 4.
Tech 5-8: Galloglaich Infantry. With two offensive morale pips and one shock morale pip, they are really, really good when it comes to breaking enemy regiments, and at that point in the game you may even start to get increased morale from things like (Defensive Ideas, Higher Prestige, AT, Power Projection, good early events like Last Jousting Tournament and Morale Advisor).
Modifiers for tech 5-8
- 0.35 at tech 5 ,0.55 at tech 6-7, 0.8 at tech 8. Fire phase damage for infantry increases, but it still is just behind in terms of damage to the shock phase. No units have fire pips at this point, and any +fire pip will be coming from the leaders. Remember though, that the fire phase is before shock phase, and 6 fire 0 shock general may not be as bad at tech 8 as you may thought. First cannons also appear at tech 7.
-0.65 at tech 5, 0.95 at tech 6-8 . Shock phase is much more important at this point, infantry will deal more damage at this point.
- 0.75 at tech 5, 1 at tech 6 and 1.25 at tech 7-8. Unit with discipline of 100% will deal 1.33 more damage than the damage modifiers would indicate at tech 5, 100% damage at tech 6, and 80% damage at tech 7-8.
- 22 at tech 5 and 24 at tech 6-8. More units can now fight at the same time on the battlefield, so you may want to consider fielding bigger unit stacks, or run more units near each other to reinforce during the battle.
- 3.0 at tech 5-8. No morale increase
- +50% Supply increase at tech 5-8. More units can station or move through provinces without suffering attrition. Important thing, especially when you consider with the fact that combat width also increases at tech 5 and 6.
Tech 9-11: Condotta Infantry. It's my personal choice in most situations, with 2 offensive shock pips, 1 defensive shock pip and 1 offensive morale and 1 defensive morale pip. Reformed Galloglaich Infantry have one more offensive morale pip at the cost of defensive shock pip, which means they are better at breaking enemy regiments, at the same time, receiving more damage during shock phase. If you have a lot of +morale modifiers, you may pick up the Galloglaich Infantry, otherwise, I would recommend Condotta, for better casaulty wise ratio. Landsknechten, are worse in terms of dealing damage (other unit types will deal increased damage against them) and their morale pips means they only hold for longer.
- 0.8 at tech 9-11 , no fire damage modifier increase.
-0.95 at tech 9-10, 1.15 at tech 11 . Shock damage is increased at the time of tech 11.
- 1.5 at tech 9-11. Damage dealt by regiments with 100% discipline is 66,(6)% of what would indicate from modifiers.
- 25 at tech 9-10 and 27 at tech 11. Slight increase in combat width.
- 3.0 at tech 9-11. No morale increase.
- +50% Supply increase at tech 9-11. No changes here.
- +25% Flanking range increase at tech 10-11. It doesn't have actual impact during battle at this point.
Tech 12-14: Free Shooter Infantry. Both units when fighting against each other have higher by one offensive morale pip than the other unit, and higher offensive shock of Free Shooter Infantry meets with increased defensive shock of the Tercio Infantry. But higher morale offensive (if you have nice +morale modifiers for your army) will allow you to shine in most cases, and 3 offensive morale means they have advantage (deal more morale damage) to most units, cavalry also. If you're struggling, and have for example low prestige, low morale due to event and/or haven't picked ideas/policies increasing religion, you may want to take Tercio, because they will suffer less casaulties during shock phase, and have better defensive morale which means, less morale damage. In most cases Free Shooter Infantry wins as better unit.
Fire damage modifier - 0.8 at tech 12-13 , 1.1 at tech 14. Fire damage increases, and with units starting to get fire pips, you may see that the fire phase starts to matter. If you're rich, or fight someone who is rich, cannons may start to appear in bigger number, and they, while still relatively weak, cannot be disregarded anymore. Watch out for fire phase, and fire oriented generals can have some merit to them.
Shock damage modifier- 1.15 at tech 12-14 . No shock damage increase at this point. Shock damage as you can see starts to lose it's big advantage over fire damage, but still due to the cavalry should be deciding factor.
Military tactics- 1.75 at tech 12-14. Damage dealt by regiments with 100% discipline is around 57,14% of what would indicate from modifiers.
Combat width - 27 at tech 12-13 and 29 at tech 14. Slight increase in combat width.
Morale- 3.0 at tech 12-14. No morale increase.
Supply increase - +100% Supply increase at tech 12-14. That change is really important, becuase you can field more easily bigger stacks without worrying to much about attrition. With bigger combat width AND artillery making some importance, think about your stack compositions.
Flanking range - +25% Flanking range increase at tech 12-14. It doesn't have actual impact during battle at this point.
Tech 15-18: Maurician Infantry. Maurician Infantry have better offensive fire (2v1) when compared to Charge Infantry, while Charge Infantry have better offensive shock (3v2) against Maurician.
Damage for shock phase is even better for infantry at this points (1.15 vs 1.1) so why this way? Answer is simple - Fire Phase is first during the battle, and ability to deal more damage during this phase, means enemy regiments will be more depleted, and as such they will deal less damage during the shock phase, than they should, which will help close the gap of their shock damage advantage. And after shock phase, there will be another fire phase where you will have advantage. Things to consider switching up, is generals. But still I would recommend sticking with Maurician Infantry in most cases.
Fire damage modifier- 1.1 at tech 15-18. No fire damage increase.
Shock damage modifier - 1.15 at tech 15-18 . No shock damage increase at this point.
Military tactics - 2.0 at tech 15-18. Damage dealt by regiments with 100% discipline is 50% of what would indicate from modifiers.
Combat width - 29 at tech 15, 30 at tech 16-17 and 32 at tech 18. Slight increase in combat width.
Morale - 4.0 at tech 15-18. Morale increases by 1.0 at the tech 15. (It means you get +33% of the base morale increase), and because all other modifiers like Military Drill, Army Tradition Prestige scales from base morale, that increase is really important - don't neglect morale.
Supply increase- +100% Supply increase at tech 15-16. +150% at tech 17-18. Don't forget about it, and update your stacks.
Flanking range- +25% Flanking range increase at tech 15-17. +50% flanking range increase at tech 18. Change matters only for Cavalry and Artillery (increase of flanking range from 2 to 3). Doesn't affect infantry.
Tech 19-22: This is tough choice. At tech 19 you could pick the Highlanders Infantry, for their awesome 4 offensive morale pips (and seeing that morale increased to 4.0 and can be really important at this point) at the cost of 1 less offensive fire versus Gustavian Infantry, and having no advantage in terms of shock over Reformed Tercio (3/2 vs 2/3). However tech 20 sees huge and massive boost to the infantry fire (+0.5) and that means Gustavian Infantry is much better at this point (mainly due to the 3 offensive fire pips) With tech 21 increasing shock damage as well by 0.5 means that Gustavian Infantry reign supreme, due to also having 3 offensive shock. TL; DR version - Gustavian Infantry best choice during tech 19-22, with Highlanders being good option for tech 19.
Fire damage modifier- 1.1 at tech 19. 1.6 at tech 20-22. This is a massive boost to the fire damage phase (around 45% damage increase), and for the brief moment (tech 20) fire damage is bigger on the infantry for the first time (beside tech 0). Fire phase, with really good artillery now starts to be really important, and with battle starting from the fire phase, devastating (good roll vs bad roll) fire phase can easily decide the course of battle.
Shock damage modifier - 1.15 at tech 19-20, 1.65 at tech 21-22 . Shock damage loses the crown on tech 20 (crown of dealing most damage by infantry), and regains biggest modifier at tech 21, but at this point shock phase being second phase during the battle, depleted regiments, deal less and less damage during this phase, and it's role and strength of this phase goes from deciding factor, to supplementary factory
Military Tactics - 2.25 at tech 19-20 and 2.5 at tech 21-22. Damage dealt by regiments with 100% discipline is respectively 44,(4)% and 40% of what would indicate from modifiers.
Combat Width- 32 at tech 19, 34 at tech 20-21 and 36 at tech 22. Slight increase in combat width.
Morale- 4.0 at tech 19-22. No change to morale at this point.
Supply increase- +200% at tech 19-22. Don't forget about it, and update your stacks, remember about backrow artillery.
Flanking range - +50% flanking range increase at tech 19-22. Change matters only for Cavalry and Artillery (increase of flanking range from 2 to 3). Doesn't affect infantry.
Tech 23-25: Line Infantry. While Caroline Infantry have better Offensive Shock, they have lower Defensive Fire, so they will receive bigger casaulties during the firing phase, and that means, there will be less men to capitalize on their shock damage phase advantage.
Fire damage modifier - 1.6 at tech 23-25. No increase in damage during this phase.
Shock damage modifier- 1.65 at tech 23-25. No increase in damage during this phase.
Miltiary Tactics - 2.75 at tech 23 and 3 at tech 24-25. Damage dealt by regiments with 100% discipline is respectively 36,(36)% and 33,(3)% of what would indicate from modifiers.
Combat width- 36 at tech 23 and 38 at tech 24-25. Slight increase in combat width.
Morale - 4.0 at tech 23-25. No change to morale at this point.
Supply Limit increase - +200% at tech 23-25. Don't forget about it, and update your stacks, remember about backrow artillery.
Flanking range - +100% flanking range increase at tech 23-25. Allows infantry to flank at 2 range, and cavalry and artillery can engage at 4 range. This means, at this point, flanking can be pretty devastating (even more than before, because earlier, less units could engage your regiments as the flanks started to falter, while now it is even more significant range).
Tech 26-27: Frederickan Infantry - if you want to be offensive. At tech 27, there is another great increase in firing damage for infantry, which leads to the fact that the more fire the better. You can alternatively think about picking Red Coat Infantry for their 4 defensive fire pips, if you want to minimise casaulties (which also helps with damage incoming from enemy artillery). At this point of the game, you're however already really big, with a lot of manpower/income to support mercenaries, so casaulties should not be a concern. However if you engage in many wars on different fronts where reinforcments may not be coming handily (not enough stacks, divided army) - pick Red Coats, they should stay longer and protect artillery from enemy slightly longer. Otherwise, and especially if you have a lot of +morale, combat ability, discipline go for Frederickan Infantry.
Fire damage modifier - 1.6 at tech 26. 2.1 at tech 27. During this time fire becomes the king of the battlefield. Watch out for enemy generals with a lot of fire pips. And 4/0 general is much better than 0/5 at this point (probably even better than 0/6).
Shock damage modifier - 1.65 at tech 26-27. No increase in damage during this phase.
Military Tactics - 3 at tech 26-27. Damage dealt by regiments with 100% discipline is 33,(3)% of what would indicate from modifiers.
Combat Width -40 at tech 26-27. Slight increase in combat width.
Morale - 5.0 at tech 26-27. Another big increase to morale (+25% base increase)
Suppy Limit Increase- +200% at tech 26 and +250% at tech 27. Don't forget about it, and update your stacks, remember about backrow artillery.
Flanking range - +100% flanking range increase at tech 27.
Tech 28-29: Impulse Infantry. Better offensive fire. You can pick once again Square Infantry - for the reasons mentioned in the section above for Red Coats.
Fire damage modifier- 2.1 at tech 28-29. No increase.
Shock damage modifier- 2.15 at tech 28-29. Damage increased in this phase, but shock is no longer deciding factor of the battles.
Miltiary Tactics- 3 at tech 28-29. Damage dealt by regiments with 100% discipline is 33,(3)% of what would indicate from modifiers.
Combat Width-40 at tech 28-29. No increase in combat width
Morale- 5.0 at tech 28-29. No increase in morale.
Supply Limit +250% at tech 28-29. No increase in here.
Flanking Range-+125% flanking range increase at tech 28-29. Slight increase that doesn't matter that much.
Tech 30-32: Another tough choice. Choice is between Drill Infantry, Jaeger Infantry, Napoleonic Square (Mixed Order Infantry is the weakest and shouldn't be picked). All mentioned units have 4 both offensive and defensive fire pips. Drill Infantry have weakest shock phase stats (3/3 vs 4/3 of both Napoleonic and Jaeger). While they have both offensive and defensive morale of 4/4. Jaeger and Napoleonic units have identical shock stats of 4/3 and reversed morale stats of each other 3/4 and 4/3. Seeing as the shock phase is less of an importance during this time of the game, and better ability to withstand morale shocks, I would probably pick Drill Infantry as the best one. Otherwise If you want to go offensive, go for Napoleonic Square
Fire damage - 2.1 at tech 30. 3.1 at tech 31-32. It is a huge increase in fire phase damage modifier.
Shock damage- 2.15 at tech 30-32. No increase
Tactics - 3.25 at tech 30-31 and 3.5 at tech 32. Damage dealt by regiments with 100% discipline respectively is around 30,77% and around of 28,57% of what would indicate from modifiers.
Combat width -40 at tech 30-32. No increase in combat width
Morale 6.0 at tech 30-32. 20% base increase in morale.
Supply increase -+250% at tech 30. +300% at tech 31-32.
Flanking range +150% flanking range increase at tech 30-32. Slight increase that doesn't matter that much for infantry.
OTHER TECH GROUPS:
Tech 0-4: Bardiche Infantry. Situation same as in terms of Western Tech group. Eastern Medieval Infantry could be considered slightly better at tech 0-3.
Tech 5-8: Eastern Militia. Only choice here.
Tech 9-11: Pike Infantry. Again only choice here.
Tech 12-14: Offensive Eastern Musketeers. Situation is similiar to the "dilemma" of Western units at tech 12-14. If you want to see my reasoning read that section.
Tech 15-18: Soldaty Infantry. Better offensive stats (fire, shock and morale). Good all-round choice.
Tech 19-22: Saxon Infantry. Only choice here. Only downgrade from the Soldaty Infantry is in terms of offensive morale.
Tech 23-25: Petrine Infantry. They're more defense oriented than Saxon Infantry from previous category, but with increased casaulties done by artillery, it is not that bad. However you may consider if you have a lot of +combat ability, discipline, morale etc. to maybe stay with Saxon Infantry, but that is something to think about, and maybe do more number crunching.
Tech 26-29: Green Coat. Only choice here. Nice upgrade from previous "dilemma".
Tech 30-32: Mass Infantry. Only choice here. Only thing that it is sad here is the loss of the defensive morale pip from Green Coat. But better fire and shock should be more than enough.
ANATOLIAN TECH GROUP:
Tech 0-4: Yaya Infantry. Only choice here.
Tech 5-8: Azab Infantry. Only choice here.
Tech 9-11. Janissary Infantry. Only choice here.
Tech 12-18. Sekban Infantry. Only choice here.
Tech 19-22. Reformed Janissary Infantry. Only choice here.
Tech 23-25. Nizami-Cedid Infantry. Only choice here.
Tech 26-29. Eastern Carabineer. Only choice here.
Tech 30-32. Eastern New Model Infantry/Eastern Carabineer. If you have much really good generals with a lot of fire pips, +combat ability and discipline, I would probably go for Eastern Carabineer from previous category. If you see you have problem with infantry holding out, and crumbling really fast (retreating) have problems with morale, choose Eastern New Model Infantry.
Tech 0-4: Muslim Footsoldier, have offensive, defensive morale and offensive shock pip. Muslim Archers lose offensive morale pip for the defensive shock pip. You may consider at tech 3 as better choice Muslim Archers, but I would in most cases suggest Footsoldiers (especially if you have +morale from piety).
Tech 5-8: Muslim Duel Infantry. Only choice here.
Tech 9-11: Shamshir Infantry. Only choice here.
Tech 12-14: Muslim Musketeer. Only choice here.
Tech 15-22: Afsharid Reformed Infantry. Only choice here.
Tech 23-25: Reformed Muslim Musketeers/Afsharid Reformed Infantry. If you have great general with a lot of fire pips, and have good combat ability, advantegoues terrain, discipline, pick previous unit (Afsharid). They have 2 more fire pips, while they are weaker during the shock phase, and have worse morale. However with better fire, they should deal more damage to enemy, and negate his shock phase advantage by depleting their regiments. With bigger casaulties piled on them, morale advantage of enemy should not be that big. Otherwise change to Reformed Muslim Musketeers.
Tech 26-29: Muslim Mass Infantry. Only choice here.
Tech 30-32: Muslim Mass Infantry will suffer less casaulties during fire phase, while will deliever less morale damage to enemy and suffer at the same time more. If you have problem with morale switch to new Muslim Rifle Infantry. Otherwise stick with Muslim Mass Infantry.
Tech 0-4: Indian Footsoldier. Only choice here.
Tech 5-8: Indian Arquebussier. At tech 5 you could consider staying with Footsoldiers, because fire damage modifier is low at tech 5, and Footsoldiers have better defensive morale, but all in all, Arquebussiers are better.
Tech 9-11: Toofangchis. It is better unit than Poligars. They have better offensive morale, while Poligars have better defensive fire, at the time where fire damage is not that big concern.
Tech 12-17: South Indian Infantry. Unit more oriented toward offense, with more offensive morale pips than Akbarid Musketeers. Reasoning of the choice more or less the same as with Free Shooter Infantry.
Tech 18-22: Deccani Musket Infantry. They have one more defensive fire pip, for the period where the fire starts to really matter, while losing one offensive morale pip. If you have a lot of morale modifiers you can however pick up the North Indian Musket Infantry.
Tech 23-25. Telingas. Only choice here.
Tech 26-29. North Indian Sepoy. Only choice here.
Tech 30-32. North Indian Drill Infantry. Only choice here.
CHINEESE TECH GROUP:
Tech 0-4: Asian Longbow for tech 0-3, while East Asian Spearmen for tech 4. Reasoning similiar to the case of Halberd Infantry vs. Western Medieval Inf.
Tech 5-8: Offensive Asian Footsoldier. Better offensive morale, when morale is really important.
Tech 9-11: Asian Arquebussier. Only choice here.
Tech 12-14: Banner Infantry. Only choice here.
Tech 15-18: Asian Mass Infantry. Only choice here.
Tech 19-25: Asian Musketeer. Only choice here.
Tech 26-32: Reformed Asian Musketeer. Only choice here.
NOMADIC TECH GROUP:
All units that appear later are better than the previous ones. No dual choices. Unit from higher mil tech = better.
SUB-SAHARAN TECH GROUP:
Tech 0-4: African Clubmen. Offensive shock vs Defensive shock of Spearmen. Choice is obvious.
Tech 5-11: South African Warrior. Chosen for both offensive shock and morale value of 2 pips.
Tech 12-14: African Plain Warriors. Best offensive value of other unit types presented at this point.
Tech 15-22: South African Musketeers. Again best offensive value.
Tech 23-25: Central African Guerillas have best offensive value, while East African Guerillas hold their ground during fire phase better, and can hold a little bit longer with their increased defensive morale.
Tech 26-29: Westernized East African Infantry. Best stats in fire phase (4/4) and really nice morale stats (3/4). Only downside to them is their low shock values of 2/2.
Tech 30-32: Westernized East African Infantry. The new unit introduced at tech 30, have lower fire phase stats (3/3) better shock values (3/3) and beter morale values of (4/4). However I don't find that losing one fire pip in both offensive and defensive to be worth it. However you may consider that African Western Franchise Infantry unit to be better.
NORTH AMERICAN TECH GROUP:
Tech 0-4: Clubmen. Choice is similiar as in Sub-Saharan tech group.
Tech 5-9: Algonkin Tomahawk Warrios. Best choice in the group. 2 pips of offensive shock and morale value.
Tech 10-13: Native American Mountain Warrios. Only choice here.
Tech 14-18: Native American Arquebussier. Only choice here.
Tech 19-25: Rifle Scout Infantry. Only choice here.
Tech 26-29: North American Guerillas. Only choice here.
Tech 30-32: American Westernized Infantry. Only choice here.
MESOAMERICAN TECH GROUP:
Tech 0-4: Mesoamerican Spearmen. Only choice here.
Tech 5-9: American Hill Warriors. Best choice in the group. 2 pips of offensive shock and morale value.
Tech 10-13: Reformed American Hill Warriors. 3 pips of offensive shock and 2 offensive morale value. Great choice.
Tech 14-18: American Hill Musketeers. Best offensive choice here.
Tech 19-25: American Guerilla Warfare. Much more casaulty oriented than the Central America Guerillas (3 offensive fire and shock, while Central Americas have 3/3 morale instead of 2/2).
Tech 26-29: Westernized American Plains Infantry. Deals more damage, while also recieves more damage than their counterpart. Depends on your modifiers,ideas. etc
Tech 30-32: Westernized Central American Infantry. Only choice here.
SOUTH AMERICAN TECH GROUP:
Tech 0-4: South American Spearmen.
Tech 5-9: Incan Slingshots/South American Forest Warriors. Slingshots deal more casaulties, while American Forest Warriors deal more morale damage. Depends on situation, morale modifiers, you may consider one of these two.
Tech 10-13: South American Arquebussier. For the slightly higher morale damage value.
Tech 14-18: Reformed American Musketeers. Only choice here.
Tech 19-25: Incan Guerilla/South American Guerilla. One have one more offensive morale pip, and another one more defensive fire pip. Choose to what you like, and need the most.
Tech 26-29: Westernized Incan Infantry. More offensive fire and offensive shock than their counterpart (at the cost of lower defensive fire and morale)
Tech 30-32: Reformed Westernized Incan Infantry. Only choice here.
