Big three (Fire, Cold, Lightning)
Cursed
Stone Skin
Extra Fast
Extra Strong
Mana Burn
Spectral Hit.
If your a caster and roll mana burn, recreate the game. If you're an elemental caster and roll that element for a terror zone, recreate the game. Cursed is doable for warlocks, as pet is mostly invincible, but if you rely on your merc, you both are in a world of hurt.
if you get Spectral hit (Seems quite rare) without sufficient resistance breaks, I'd reroll the game. Everything will be highly resistant or immune to your damage.
So spectral would make the tankiest demon so long as the demon skill is high enough to give stone skin etc