Since the game seems to favor having a ****load of archers in EVERY army you face, I'm only interested in troops equipped with shields.
Because of this, I don't care for the Vaegirs. Swadian infantry have shields, and the Vaegir infantry usually doesn't since they run around with 2handed axes.
Since their Cavalry is more or less the same, I default to Swadians.
I don't like the Nords because too many of their "infantry" units come with ranged weapons, and when you tell them to charge, half your guys hang back and shoot instead. This is particularly annoying in sieges, where shooting is not very useful. If the game's tactical menu had a way of FORCING them to charge, this wouldn't be a problem.
Of all the armies, the Swadians are probably the most well-rounded and don't suffer the shield problem of the Vaegirs.
Next time I play, I might try the Rhodocks, who seem to be a strong infantry army, which I actually prefer. Cavalry armies are pretty boring because they're very powerful. They're also frustrating when you have to fight on Mountainous terrain.