Every time I play Bannor I always go for The Order, however, after my last game I am starting to think that Empyrean might actually be a better fit. The Order fits well thematically and Undying Order is a great spell, but I find that Bannor, because of the mana types they start with, has a deficiency with respect to destructive magic capable of affecting an entire stack, which can make taking a strongly defended city exceedingly tough. Empyrean seems to cover this deficiency with Chalids Pillar of Fire and Luridus Crown of Brilliance. You miss out on Undying Order, which is really nice, but I think Crown of Brilliance makes up for it, and when I go into world conquest mode with Theocracy and Crusade I generally dont have happiness problems anyway. You also miss out on Vallin and Sphenor, but Chalid is at least as good of a hero as Sphenor, in my opinion. I havent found much use for Crusaders, maybe if I was fighting Sheam or Hyboram, other than that I almost always build champions instead.