I'd choose the power to change probability. 100% chance of finding a million dollars, 0% chance of death. Simple as that. 100% chance of being invisible, of flying or any number of things I want, and I could change those at any point in time so that I could become visible again or whatever I felt like. Fun huh?
That would be pretty cool but at what point do you get bored because nothing goes wrong for you. I think a perfect life is a boring life