To be honest, I play classes more for flavor that power or even playstyle. My two mains are as different as can be--a mage and a prot/fury warrior, and I love them both. I like my affliction warlock as well--but again, mainly for the flavor. To me, I play a warlock because it's different from other classes--so I'll go with the spec that has a different focus from hunters and mages. Keep in mind, I'm still referring to flavor more than actual mechanics. I could care less about which classes are the most powerful--I don't do anything higher than heroics anyway.

I guess I've always liked the underdog and the sense of danger. As a mage, I'm relying totally on my intelligence to save me from things much stronger than I am. I don't "defend" myself as much as simply blast away, run away, and freeze them, hoping to just barely squeeze out victory. Lots of people don't like that feel--and lots of people don't like Frodo as much as Aragorn. That's just me though...

Even as a warrior, I still get that sense of peril. As fury, I'm not very defensive at all--I'm just wailing on things to shock-and-awe them to death before they can react. Even as prot, I'm running (read-intercepting) back and forth, desperately trying to keep the monsters away from my friends, without being able to rely on Holy, Natural, or Runic magic.