A whole lot of Anbennar.
Arg-Ôrdstun is fun if you like a whole lot of noble rebels, assuming direct control of Aul-Dwarov, being completely out of touch and creating a monopoly of precious gems. Its certainly more fun than Orlghovar, whole thing was kind of a let down tbh, a whole lot of pain for some fairly strong buffs, but nothing quite worth the effort. Though my baseline of "strong buffs" is Ovdal Kanzad.
And the only other country to impress me was Feiten with its crazy modifiers (+6 movement speed to fleets? You can sail around the world in 4 months! Don't forget to click "the funny decision" to instantly win any siege with your special merc comapny.) I should play Feiten again.