I'd say either teleportation or flight. Anything that can help me get around faster would be amazing. No more bus rides to work for me.
ghost powers! basically: intangibility, invisibility, and flight. Although invisibility is just intangibility being applied to light waves... but I digress
I'm patient enough to be okay with not having teleportation or flight, and no way do I want to read minds. My preferred power? Healing. I'll leave it at that one-word answer. Does that mean self-regeneration? Healing hands upon others? Physical, emotional? I don't even know. Hopefully all of the above, but we could all go for some more health and comfort.
I'd either like telepathy or nat 18 + 2 (racial) charisma. Knowing what others are thinking and/or the ability to convince them to help you seems powerful to me. Bonus is they might have a superpower of their own that you can utilize.
The Flash. His superpowers would be something else! Very cool to speed like lightning about the place.