I don't think I'd want to fly, if you don't have super speed with it, it's just the speed of walking, if you go to high, you'll lose oxegyn, and if you go too low kids will hid you with paint balls. Not to mention you're legs will go through your shoulders the first time you try landing on your legs. Then again if you breath underwater, you won't be protected from sea creatures like sharks, and you still have to prattle through the water which could get tiring, not to mention the deep creepy parts no man has ever explored. If I had to chose one, breathing underwater, at least then I can freak people out by pretending to drown at a public pool XD.
Watch and learn: http://www.cracked.com/video_18289_the-best-super-power-is-not-what-you-think.html