[Vicious Love]

I imagine fire snakes are around slot #4 or #5 on my units list. Not because they're a particularly efficient use of gems, but because they're a particularly efficient use of fire gems. When your only alternatives are artillery spells, items, and inefficient battlefield boosts, there's something to be said for summoning. Or alchemy, I suppose, but I find the snakes more effective than most troops.

Clay men and mechanical men are definitely on the list as well, and everyone loves devils, ideally via contract.

As for commanders, there's definitely a vampire lord somewhere on the list, no equipment required. They make decent thugs, but their primary purpose is to muster immortal, flying, lifedraining goon squads, for all your defensive needs. Speaking of immortal units, wraith lords are... well, if they're on the list, they're #5. Very pricey, but useful for reinforcing defenses within your dominion, especially if you're the sort of undead nation that can't just cough up the gold for a few skeleton spammers. Spectres and lamia queens are on the list, too, for easy access to pretty much every path of magic. And you just can't beat the price tag on a Tartarian, even without the Gift of Health or the Chalice.

Edit: Hmm... odd how there are no ghosts on my list. I suppose I'll drop mechanical men down to #6 to make room for them. Always preferred specialized troops, anyway, it's just hard to say "no" to those across-the-board resistances.