This is what my impressions are:
Vlandia: Solid all around for any playstyle, really - you can use this to level up troops for donations, garrisons, and clan parties even after getting top tier troops yourself.
Sturgia: Highly niche and the snow slows your map speed too much, so I don't even like playing in it to try to utilize this.
Empire: It seems like the real bonus for Empire is town loyalty just due to how many more cities are Empire culture.
Aserai: I kinda think it's garbage and would rather be Khuzait for trading.
Khuzait: I think if you're focused on just knocking parties on the map out, this is the strongest overall provided you have the party composition to benefit from it.
Battania: This is a good one for general mobility, escaping, chasing, and more foot soldier heavy parties that wouldn't pick Khuzait.
Of course I've played some factions more than others, so I may be overlooking the utility of some of them.
Vlandia: Solid all around for any playstyle, really - you can use this to level up troops for donations, garrisons, and clan parties even after getting top tier troops yourself.
Sturgia: Highly niche and the snow slows your map speed too much, so I don't even like playing in it to try to utilize this.
Empire: It seems like the real bonus for Empire is town loyalty just due to how many more cities are Empire culture.
Aserai: I kinda think it's garbage and would rather be Khuzait for trading.
Khuzait: I think if you're focused on just knocking parties on the map out, this is the strongest overall provided you have the party composition to benefit from it.
Battania: This is a good one for general mobility, escaping, chasing, and more foot soldier heavy parties that wouldn't pick Khuzait.
Of course I've played some factions more than others, so I may be overlooking the utility of some of them.