[Infiltrator]

Meh, I'm using blacks. It's hard to get one killed, unless they are alone in the enemy lines. I use the demonologist's life drain on my other units since they are most often the targets.

Also, when your blacks eat up a retaliation of thousands of fire/magical based units as a two-digit number, you just have to feel good about it.

Having the highest base resistances and att/def, as well as being impervious to all spells, they are very independent and you can focus on maintaining your other units. Lowering initiative of the enemies is also very important, I almost always get to act with all of my units before the enemy gets the chance to act with their fastest one. Highest base att/def in the game means having a high morale gives them absurd bonuses to those stats.