Don't quite know if this is considered a spoiler or not, but I've been meaning to ask the question and this section has this visage of being better safe than sorry.

Simple question for a lot of possible answers. I'm looking for general overall effectiveness as opposed to effective, but only against x enemies.

Thought I'd jump in and say I'm looking for info on this aswell.

Well first. if you are on PC be sure to spawn the enemy new for you because of issues involving leveling.
As for the answer for your question:

Savos Aren and Orchendor.
Savos Aren is capable of summoning dremora lords.
Orchendor has 100% magic resist. You can also equip him with sanguine rose.

Another great alternative if you don't want to ressurect the archmage (though technically its still canon)
Sebastian Lort.

All of them are incredibly beastly mages at high levels.



If you AREN'T on pc. Any high level mage enemy you happen to face that is NOT a necromancy or conjuror (because for some reason anything those guys summon seem to be aggressive towards you). This is because special unique characters are spawned when you first enter their cell. Its highly possible that you may have entered the cell of a certain person but never met them and they are still at some extremely low level because of it .



Edit: I will warn you ahead of time I really recommend killing orchendor, savos aren, or sebastian lort with console commands. Trying to kill them when you spawn them at very high levels is a VERY difficult task for any person without incredibly high magic resist or spell absorption. You have been warned.
Also just a heads up if you want to be able to dead thrall actually useful people you need to mod your game to allow the spell to affect high level mobs. Otherwise you are stuck with dead thralling people that are around level 30 and they svck at end game.

Unfortunately I use a console so Savos is out, but duly noted for the future. The other two sound good though, since I've yet to bother completing daedric quests with this character.

I appreciate your speedy & detailed response DrDarkness.