I usually play kergit...
my games are always like this:
First Dhirim goes down to the kergits, then they struggle to keep it, and every war it is being captured by another faction.
rhodok and sarranid dont capture much from one another, mostly the struggle for Shariz.
Nords are really bad, they immediately lose their southern fiefs to veagir.
Swadians are worst, really good knigts, but everyone attacks them... and they lose fiefs one after another.
veagir, nice faction, never really in trouble, they just keep up like rodok.
Sarranid, really nice faction, but when at war with kergit and rhodok they lose fiefs...
kergit, best faction if they dont expand much in the early game.