That's not such a difficult one, as the alternative to the ability of breathing underwater costs about a thousand dollars and a pinch worth of scuba gear and training, and you're free to go where ever that's not too close to dangerous things, whereas the alternative to the ability to flight costs you about twenty-thousand dollars worth of training and a little 172 to fly, while you're subjected to very strict laws and will still have to pay for fuel and upkeep.
Even that aside, I think I'd still rather fly tho. The world up here is just more interesting than the one underwater, imo.
What's the best cookies?