I really enjoy a lot of units. My elite Cave Drake who leads an elite team around on his flying carpet is a favorite. So is Henrik the indie priest who won the deathmatch tournament, and is now a middleweight melee supercombattant in full black steel plate. Arco priestesses are great to have, especially if you aren't Arco! Succubi are great when they're on your side. Mictlipoctli, before I accidentally burned him to cinders with my demonic heat aura... ooops. Dragons. Blood summons (the one with four arms). Way too many different kinds of units to have a single favorite. Many are beloved though.
PvK