I'd have to go with Necromancy.
Every game I play, I will invariably play the necromantic class (Necromancer in GW2, Death Knight in WoW, Shadow Knight + Necromancer in EQ2, Necromancer/Poison Mastermind in CoV etc. Heck, I even really like playing some of the undead/zombie/unliving characters in Dota 2 such as Pudge, Lifestealer, Necrolyte, Undying, Clinkz etc)
Necromancy is pretty cool, the stuff you can do with it just really appeal to me:
- Summoning armies of undead minions to unquestioningly following your ever order (Also, can create abominations using mixed parts/slabs of flesh for specific tasks... Such as perhaps a coffee table that will walk alongside you!)
- Drain life from things that disinterest or annoy you... Get rid of pesky weeds and annoying insects without having to spend money on fancy products!
- Enhance your own abilities, either by just siphoning it from someone/something else or by creating temporary boosts for a cost (Not unlike a lot of addictive recreational drugs?)
- Power over life and death? Heck yeah! Though easy to abuse...
- Resistance/immunity to disease and infection? Awesome, being ill is not fun (Bonus points if you can keep making people you don't like sick... Not even some hard-core disease, perhaps just give them a cold at a really annoying time...)