Ulm / Iron Faith
I just like the idea of banishing all mages from the game
I'm having fun with my Mictlan AAR, but frankly the only reason I chose Mictlan is their awesome (strategically speaking) starting position in the World War scenario (whereas Ulm's suck big time).
As for second place, I'd say Pythium / Serpent Cult. I love gladiators, and I love hydras, especially blessed ones