I would personally go for teleportation. I think the idea of being able to snap your fingers and put yourself instantly anywhere in the world would be awesome (that closely followed by time travel). What say you?
the ability to improve my own luck or other people's luck on a daily basis, where good things can happen big or small, like small lottery winnings, scoring well on a multiple choice exam, meeting the girl you wanted to talk to but miss the opportunity in the past, etc