Ok, not a faction disscusion, simply units you loved in MTW.
Highland Clansman-even with scotland a faction, I hope this will be a regional unit. It was always much fun to rasie large armies of Scots and cursh Europe under my heel, while the motherland simply increased its economy.
Viking Era stuff: The vikings and viking landsmen are a must have. The vikings may be comming out of date, but they are still fun as hell to use!
Slav Spearmen: I know you slavs want more than this crapped down unit, but gameplay wise, it proved a good garrisoning force in the east over the usual peasants.
Knights Templar: Nuff said really, this guys are simply gods among men.
Ca make some steppe nomad units(Cumans, pechengs etc) and I will be happy!