6. Batannians (Celts) have cool rhomphaia-wielding Savages. But no heavy cav (my fav class), infantry is mediocre, and while the expensive Fiann's longbow is powerful, takes too long to draw - in the meantime, Imperial or Aserai archer will pepper you with arrows. 
5. Khuzaits (steppe nomads) have specialized horse archer, good heavy Lancer, and fair infantry with maces & big square shield for low price (120 gold). Khan's Guard not better than Imperial or Aserai equiv, but costs more. Not a superlative faction, but competitive against any.
4. Imperials (Byzantines) have Palatine Guard, perhaps the best archers - heavy armor, quick draw & carries menavlion (so can hold one's own in melee). Heavy armor Cataphracts with long kontos are ultimate "anti-cav" cavalry, but no lance capabilities & game's priciest unit.
3. Aserai (Saracens) Veteran archers are almost as good as Palatines, and Mamluk lancers as good as any other heavy cav. Only problem is no armored infantry, like the excellent Imperial Legionary with his high damage (though limited) pilas.
2. Vlandia (Franks) have dominant heavy cavalry Knights, cheap Vanguard with lances, and heavy punching Sharpshooter crossbowmen with armor & thick panisse shields. This faction can both take deal and take hardcore damage.
1. Sturgians (Rus/Norse) fav faction & not cuz I'm 🇷🇺. Light archier Hunters are cheap but still competitive, best heavy infantry Varyags, insanely fun Berserker axemen, & heavy cav Druzhinniki that can go lance to lance with Knights, Mamluks, or Lancers. True adepts of Khorne!
