Any, at all, and you're still you when you chose, you just have this heroes' powers
I definitely would be Martian Manhunter. The ability to shapeshift at will and to phase through solid objects, as well as being able to fly, reading minds and shit would be so helpful in life.
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I'd say myself, but I'm no hero. Well I've saved your a$$es a few times, but I didn't do it out of the "goodness of my heart." So I'll go with the next best thing. One Above All.