I pretty much only use might mercs. Only time I don't is with my blizz sorc (defiance).
In reply to the other post:
I don't know about Doom for a necro that summons (i.e. skeles, resurect) With the cold damage you wouldn't have as much bodys lying around. You would need them for either your army, or for CE. Doom works well on other charaters' mercs, like a Strafe/Mulit Zon or any Melee build.
You could always go A2 Thorns Merc for a summoner...
Whats a good merc for a bot blizz sorc (if i ever get rishodi's to work) i've been tryin to lvl a a2 freeze merc but its a bitch and he wont even have his aura on when and if im bottin right?
If you have set up your bot correctly I doubt your merc's Aura will every activate. So the keys is DR/Life/DMG, My merc is using Levi, Eth GAze, and an Eth Reaper's toll, and he does about 3.5k dmg. he's a defiance merc, soon i'm going to put my Doom Polearm on him tho.