Good question. I could go with reality warping, but what I'd probably end up doing is give myself miscellaneous powers and lock away the rest of my power for emergencies only.
Teleportation would be convenient, but it'd make things... less interesting. I like travelling, even if it takes a while sometimes. Short "flash steps" would be nice, though. But not, like, burst of speed flash steps, but short-range teleportation.
Regenerative, unaging immortality would by good to have, but only if I get to die eventually somehow, preferably of my own free will. Like, I can only die through suicide. Living through the apocalypse would be... problematic. Also, living on after being chopped in half would suck, too, so I'd have to regenerate that...
I would like Misaka-style electric powers, but they might mess with my electronic and magnetic devices and objects a bit. Still, it'd be cool to launch a coin like a railgun, though I don't think it'd have much application in this day and age.
Shapeshifting, on the other hand, would have many possible applications. Besides, I would be able to look however I want to look. It'd be pretty nice.
Another thing with tons of applications: the ability to mimic and copy things that I see other people do, perfectly. That'd be super awesome for a guy like me, who hates practicing. XD
Really, I can't decide...