Invincibility. No question. Want to see the bottom of the ocean? Tie some rocks to your feat. Want to experience flight? Jump out of a plane with no chute. Or step outside of the space shuttle with no suit. Explore the center of the sun or anywhere you want. And finally have the courage to tell those talkers in movie theaters to SHUT UP!!!!
(Okay, so invincibility might not be the best thing for my character...)
Invisibility (including the ability to suppress your own sounds and thermal signature), combined with controllable intangibility. Go anywhere. Locked door? no problem!
Okay, so that invisibility is a bit overpowered, isn't it?