I'd pick a Green Lantern ring. I could do anything Superman could do to the maximum meaningful degree in the real world. Meaning I wouldn't need the ability to move or burn an entire planet with no villains or crazy circumstances that happen in the comics.
Depending on how well the ring takes care of you, you're lifespan would probably approach 100 years and in that time whoever wants it can probably figure out immortality or at least extended life.