First yes you can break free, you can even have your own Lord under you now since of the much more flexible diplomacy model.
For faction I will list their best unit and also those I think to be cost efficient.
Rhodok: Inspired by Northern Italy and Swiss, best unit are sergeant (outside of Nord it is the best infantry) and sharpshooter, cost efficient about anything in the crossbowman tree, they have by far the range unit best equip to hold melee in both equipment and stat, but would say the trained crossbowman the most cost efficient of the three, with the right defensive structure they can take care of any assault force by themselves without any other unit type has support with barely any lost during a manual defense and for quite a low cost. Most of their unit go around with a pavise shield.
Nord: Inspired by the Norse (Viking), best infantry in the at any tier and only faction with a tier 6 unit (Huscarl), lot of their infantry has chance of throwing weapon, their archer are somewhat lacking in equipment compared to other faction. Cost efficient I would say trained footman and warrior. About all their infantry go around with a round shield.
P.S. All the unit of those two faction tend to have high athletic, lot of other faction infantry and range unit tend to have none. Help both the battle and map movement speed.
Swadia: continental Western Europe (France or HRE), best unit the Swadian Knight, most heavily armored unit in game on an armored horse, yield sword, lance and cavalry heater shield (in other word what you expect from a knight in about any game =p), their infantry is has heavily armored but go around with normal heater shield but is one of the slowest unit in game since of those heavy equipment and lack of athletic skill. Crossbowman are decent nothing really to distinguish them or put them under other faction range unit. Cost efficient unit militia and men-at-arm, militia are basically infantry that got 50% to come equip with a crossbow, you want a cheap unit to swarm in garrison for tactical advantage, they are the answer, they got very decent equipment for been tier 2 and in garrison they cost like 1-3 denars each depending on leadership skill. They also nice to simply bolster army size if you don't care about movement speed, basically let you go around with less cavalry since with them bolstering rank you reduce enemy tactical advantage so get higher number of troop on battlefield for a low cost. This is really a cost saving unit. The men-at-arm are there simply because they are the most cost efficient heavy cavalry.
Vaegir: Slavic Europe, best unit are the archer supported by decent infantry and cavalry, their knight and infantry are slightly less armored then Swadian and tend to prefer 2 handed weaponry, their T2 unit is poor compared to most faction but they got a very versatile t3 (skirmicher on archer side, veteran on infantry/cavalry side) the veteran have 50% chance to come with an horse at start of battle, so now with the new command syste, they are not has good in proper command condition has other unit but outside of Khergit I don't think you will find a better swarm that contain cavalry that easy to train with simple training skill in a few day from simple recruit. But not really the faction I know the best, so other should be giving tip.
Khergit: Mongol or Turk Khanate. Strategy fast moving cavalry swarm (no faction move faster on both battlefield and map), if you want cost efficient cavalry they are the one to see, they got the best battlefield T2 of all faction if you ask me, those skirmisher might not be great at dealing damage but they are very good at their job, breaking enemy rank so the horseman/lancer can swarm in do the killing. Their horse archer and the veteran one are really the best there is at doing skirmish. Lancer which is medium cavalry, are well armored and armed, but their lack of heavy horse (they have courser) make them poorly suited at charging enemy formation, they much better once enemy broken or at running after other cavalry. At very start of the game until you got enough level and money to build a decent sized army, they are really the best recruitment ground, for you will have both cost efficient unit (everything they got is cost efficient), while stay fast on map which will let you evade force that might endanger you. Just try to avoid mountain and forest for your fighting, while the desert is the nicest playground ever for Khergit (trust me with a Khergit based army find the desert bandit camp and hunt around it, it will best one of the safest xp you can get and they much easier to find and kill then sea raider [also check in tavern to see if a guild master offer bounty for bandit from time to time, that an easy 1k denar if you found the desert bandit camp, they will always come back toward it after a while, they also outrun Sarranid Lord most of the time, so low chance a Lord will come to kill them and fail quest])
Sarranid: Northern Africa Sultanate, best unit the Mameluke without contest, heavy cavalry, basically same thing then Swadian knight but trade a bit of defense for offense, they are both deadly on foot and on their horse (and since they lack heavy infantry they are your heavy infantry for siege =p). Basically they foot army is based on doing skirmish and will not survive prolonged melee by themselves, but outside of Rhodok and Nord I think they are the only infantry with decent movement speed. So basically just use them to tie up the approaching enemy so cavalry can be most efficient then order retreat so they don't get all kill if needed, they should be able to outrun a Nord, since they wear heavy equipment, so the cavalry finish up the work. Their foot archer are also the only one to compare with Vaegir from what I know. But for this faction it mostly all guess from the little I know, since I never was in war with them yet and didn't play my character I plan to side with them yet, just did some custom battle with them. But like I said I am pretty sure it is a skirmish footman and aggressive cavalry army (their horse have the best maneuverability, so they don't lose much speed except on very bad terrain and seem to turn on dime compared to heavy horse =p).
P.S equipment might not fully be exact for equipment slightly messed up since a bit before release from what I know. For example see unit going turtle (unit wearing 2 shield, one on arm like normal, other left on back) which is very odd on AI unit, for they never did so before, and which I also refuse to do because it stupid for a regular fighter to encumber himself with multiple shield during fight (that what shield-bearer are for when situation require it =p)
