I would want invisibility. Primarily for safety. If I am leaving my house, there are so many times in a typical day for me when Not Being Seen would be so much better. It would up my safety level so much. Would be great at the airport, too, when there's a long TSA line.

Flying would be way more fun, but invisibility would be my pick.

(Also, I'm not interested in any of the ways most people would think invisibility was "useful".)