I usually did it this way:
Life:
spearman (ballista is cool, but slow)
monk
Knight (plentiful, cheap, first strike)

Death:
ghost
vampire
undead dragon

Nature:
elves
griffins (much cooler than unicorns, they fly and have infinite retaliation)
magic dragons or phoenixes, it depends;
from the portal I usually took water elementals, because they hit with magic + quicksand (one of the coolest spells)

Might:
harpies
cyclopes (DEFINITELY!!!!)
birds
And I also used this trick - so that berserkers wouldn't die for nothing, I fought without them, stockpiling them in the Castle and using them only in serious battles

Chaos:
medusas
nightmares
dragons (:))

Order:
mage
djinn
and here is the toughest alternative - titan or golem-dragon?... I used to always take dragons, then it started to vary