I would like to have a wide variety of weak/low level powers. Strength and reliablity are not impressive, but the versitility means that I will get my use out of them, and could handle any situation.
My vote goes to a form of Energy manipulation which would allow for levitation, shields, small energy bolts, various other uses. Think Raven from Teen Titans, only broadened out a little more. However the thread title is if "I could have ONE power"... So I'm disqualified.
We come in peace, Shoot to kill.