If I could choose to have one superpower, I would pick the ability to fly. Flying sounds like it would be amazing due to all of the new opportunities it offers. For example, instead of having to climb a large mountain, you could simply fly to the peak and enjoy the amazing view.
Flight would be pretty cool. But it seems like you would need a lot of other powers to use it effectively. If you tried just flying to the top of Mount Everest, or any 8000m mountain for example you would find yourself unconscious, frozen and dead within minutes, even if you wore winter gear. If it was a high speed flight, your body would need to be superhumanly strong. Wouldn’t want to hit a bird at the speed of sound, or a fleck of dust from Africa to hit you in the eyeball and explode it.
For super powers I would want the ability to fully control and create all electromagnetic fields, because that governs basically all chemical reactions. You could become an alchemist and convert dirt into gold, even if it took several evolutions of elements. You could create lightning bolts. You could power machinery like a mecha, or produce the thrust for jet engines to fly into deep space. You could cause the electrical bonds holding people, or their machinery together to break apart, dissolving the heroes enemies into goo. You could create force fields that stop bullets or explosions. You could fly by changing your magnetic field, while creating a shield around yourself, while ensuring you can make oxygen from nothing.