Done a quick look at all of the factions, minus the Orcs.
Doing a coop campaign as Vampire counts and loving them so far, the attrition and corruption isnt too OP nor does it fuck you over, just requires you to plan ahead a bit more. Empire is the tutorial campaign for the first ~5-10 turns, but i fucked myself over by trying to form too many confederations and somehow getting 2 dwarven factions and Middenheim to come invade my lands, not a good idea. Dwarves are a good laugh except their missile units are ridiculously powerful, and the infantry are pretty tough, hardly taking any casualties due to high armour and melee defence.
But the biggest disappointment is definitely chaos. Although their units look the best and they have some of the best units in the game, the campaign is just too boring. Im not a big fan of hordes anyways but Chaos campaigns are too quick, I find it is literally, move raid, move raid, move raid and in the beginning its chaos units v marauders so theres very little challenge. But thats just my opinion on Chaos as i really do not like the horde movement or factions ways.
But id place vamps top, then dwarves so far. But loving the game all in all, much smoother, AI are actually smart in this one, doing flanking attacks, attacking their strong vs weak units, and the AI on the campaign map actually uses stances and their armies in a smartish fashion.