Inquisitors vs. demonologists vs. archmages

[dougrob173]

I've been using Inquisitors since I started the game, but now that I'm at level 35 using a paladin hero with max resurrection skill and the resurrection spell, and Paladin units (yes I know overkill on the resurrection), I rarely need the Inquisitor's skill. So I'm thinking of switching them with demonologists or archmages. Just wanted to get other's opinions on advantages/disadvantages or each stack.

Also since the demonologists are rare, I heard that the sacrifice spell can be used to increase the unit #s. I tried the spell a couple times, but it would only let me reinforce the unit that had casualties. So is the spell limited to only increase the # of units that you started the battle with?

Thanks.