@Anthony/Alex - I never did read much in the way of comic books, but I always preferred the DC universe to Marvel. Can't quite put my finger on it.
Anyways, my favourite hero was always Superman when I was a kid. Seemingly unstoppable from a physical sense, each meaningful battle for him was a moral battle, and when I was younger, I liked that he always did the "right" thing. Only years later did I realize I connected much more with Dr. Manhattan from "The Watchmen". Another being with quasi godlike power, yet he was seemingly indifferent towards the struggles of people, and couldn't curb his curiosity about the universe in order to help them. Not saying that I don't care about people, of course, but give ME godlike power and I'm not sure that would remain the same.
Superman is one of my favorites, but he'd be at a disadvantage in a high gravity environment, or a planet with a red sun, or in the presence of kryptonite. Now Doctor Manhattan is pretty cool.
My preferred superpower would be Hulk's super strength and it's attendant invulnerability.