Best in class - by faction

[Miracle]

Building upon what Foz has said, I think it's important to include other characteristics besides in-game stats into the definition of "best." The best units should perform well in each of the categories below:

• Combat Ability - ability to receive and deal damage
• Versatility and Adaptability - ability to attack different types of units with moderate to high proficiency and doing so in most terrain conditions
• Training and Upkeep Cost
• Building and Technology Requirements
• Upgradabilty and Potential Exp Bonuses - what level armor the unit can be upgraded to and how easy it is for its faction to provide exp from guilds and buildings
• Unit Size and Hitpoints
• Range, Ammo and Accuracy (if applicable)
• Special Abilities
• Marching and Running Speed
• Morale, Stamina, Discipline and Training
• Recruitment Pool and Replenishment Rate
• Aesthetics - hey it's gotta look cool, right?

Examples:

What is the best Spanish swordsmen unit?

Answer: Swordsmen Militia. SM retain 75%-85% of the combat ability of DFK's while requiring 70% of the training cost and only 0%-44% of the upkeep cost. Since army upkeep is normally the biggest part of the expenses, this is a big deal. They require large city-level militia drill squares to build, which are more plentiful in the high/late eras than fortresses (most players have more cities than castles). In addition, wealthy, sea-accessible regions like Italy and Britain tend to have very well-developed cities making retraining SM easier. SM can be upgraded to heavy mail which gives +2 armor as opposed to the +1 from DFK's partial plate. On the downside, SM's may rout sooner against cavalry charges and tire more quickly in extended melees than DFK, but the former is avoidable and the latter is negligible.

What HA are better, Byzantine Vardariotai or Egyptian Mamluk Archers?

Answer: This may be surprising but I believe Mamluk Archers are better. The chief reason why is spammability. Vards are limited to a recruitment pool of two units at castles and three at fortresses. Upgrading to citadel walls and the stables line does nothing to increase the pool. In contrast Mamluk Archers' pool can be increased from citadel walls, the stables line and Sultan's Racing Tracks in cities. So it becomes far easier to spam MA, especially in High/Late. MA's combat abilities are still quite formidable compared to Vards so you're not losing out too much. It's also offset somewhat because it's far easier for Egypt to obtain a Horse Breeder's Guild HQ than Byzantium. Price is not an issue because both Egypt and Byzantium can hold very rich cities and resources early on. MA are slower than Vards but their bow range makes that less important. So the question comes down to, would you rather have one Vard and one Byzantine Cavalry, or two Mamluk Archers with exp? The choice becomes obvious.

[HoreTore]

Polish army before you hit Citadels and gunpowder:

20 Polish nobles. No need for anything else at all, although you could throw in some order knights for fun.

[andrewt]

The problem is the quality of DFK. The next in line, chivalric knights, require way more expensive buildings and only gives 1 additional armor. For something that has 21 total defense, 1 additional armor is pretty pathetic. Morale is the same, attack is the same, charge is the same, etc. I forgot the stat of mailed knights but I think there's more improvement there. Another problem I saw with western factions is that almost all the knights units past mailed knights are similar. There isn't much variety.

[Shahed]

That's true, more differentiation might be good.

[Empirate]

Hungarian DCK actually have inferior stats to DFK, if there isn't something I've overlooked - this might be due to armor upgrades being available earlier or something like that. However, DCK seem to perform better than DFK as far as I have found. Maybe there is some hidden variable entering into the equation as well. Also, DCK have slightly less upkeep... for what it's worth.

I'll try a list for Hungary:
Swordsmen: DCK
Spearmen: Pavese Spearman
Foot Missile: Pavese Crossbow Militia
Heavy Cavalry: Hospitaller Knights / Royal Banderium
Missile Cavalry: Hungarian Nobles
Artillery: Basilisk (Serpentine vs. troops)

[Foz]

Hungarian DCK actually have inferior stats to DFK, if there isn't something I've overlooked - this might be due to armor upgrades being available earlier or something like that. However, DCK seem to perform better than DFK as far as I have found. Maybe there is some hidden variable entering into the equation as well. Also, DCK have slightly less upkeep... for what it's worth.

Actually they have the same upkeep... and DCK cost a bit more to recruit.

DCK stats, while somewhat inferior, do break down differently than DFK stats (in a good way).

DFK armor/skill/shield:
7/8/6
DCK armor/skill/shield:
8/8/3

This gives DFK the following armors:
Front - 21
Side - 18
Rear - 7

and DCK have:
Front - 19
Side - 17/18 (I don't know whether the game rounds 1.5 up or down)
Rear - 8

So they're nearly as good as DFK, just not quite. The only other possible explanation for DCK performing better than DFK would be if they had better (faster) animations which allowed them to attack more often. If they do, I haven't noticed it, and I seem to have DFKs beating DCKs routinely in 1v1 battles, so I'm guessing you have simply had a few weird experiences that have led you to false conclusions.

Or I suppose you could be using a non-1.2 version of the game, or a 1.2 that patched incorrectly. If your game still has the shield bug (pre-1.2), then DCKs would probably be better because they have substantially less shield points, meaning it would drag them down less and they'd probably end up more effective.

In any case, you should probably run DFK (any faction, they're identical) against Hungarian DCK a few times and see what happens for you. As I said the DFKs beat them for me, so if they don't for you then maybe something is up with your game.