For some reason the question "If you could have any superpower, what would it be?" seems to come up a lot in life. At least in my life, anyway. Job interviews, friendly conversations, internet boards, and psych evaluations all seem to think that the answer to this question will reveal something significant about your deeper soul. But actually, it is a trick question. The obvious answer is "omnipotence." Why pick "flight" when you could pick "flight and everything else?" If I could just have the power to do whatever I want whenever I want, problem solved, right?
Of course the other trick part of this question is that nobody should ever be given superpowers that wants them. Much in the same way that no one who actually wants to be the president should ever, in any circumstance, ever actually become the president, simply wanting a superpower is proof that you shouldn't have it. There are two types of superheroes out there: those that got their powers by accident and are constantly cursed by them (Spider-Man, The Flash, any of the X-Men), and those who worked really hard to get their powers, and subsequently are jerks (Batman, The Punisher, anyone working for Rupert Murdoch). I'm not saying that Batman doesn't do some good out there, but as a general rule, if you desire more power than your fellow man, it's probably not good news for your fellow man.
So putting aside the fact that if you actually had superpowers you would only try to use them for sex and/or money, let's take a look at why you need more than one power to actually do anything cool anyway.
Honestly, what good is flight going to do you? The Air Force would immediately shoot you down, and you would constantly be in the way of airplanes. Are you assuming that flight comes with super speed to avoid incoming aircraft, or super strength to possibly fend off the U.S. military? And do you have super-no-need-of-air for flying up super high? No, if you actually just had flight, the best you could ever do would be to hover around your neighborhood, and maybe get things out of trees easily. And you could probably get on Letterman.
Unless super speed comes with super durability, you are probably not going to want to run that fast, because you are going to crash into things a lot, especially at first. Society does not build things for super fast people. You know when you look at really old buildings and the door frames and ceilings are all lower because people were shorter back then? Well, if everyone was fast, we would make hallways longer, corners less sharp, and the designs would reflect our new speed. But everyone is not fast. Getting around would be like being a 6'5" person trying to get around a few centuries ago. They wouldn't fit in anything, and you would be crashing a lot. The only place you could really cut loose would be the highway, and maybe some wide open wilderness, so unless you want a lot of speeding tickets for running, or want to move to a savannah, speed might not be so great. And as an added bonus, you would be super annoyed at everyone else going slow all the time.
What reason is there for this power other than sneaking into bank vaults and opposite sex locker rooms? No, the only reason for this power is if you are a criminal. Even the Invisible Woman has other powers to offset the creepiness of this power. She can also make force fields, which is useful if you want this power for hiding purposes. Because really, if you are trying to hide, or move around stealthily, people are going to bump into you a lot. You would need some sort of force field if you really wanted to stay hidden. So in short, there is no reason any decent person would ever choose this power. If someone gives this as their answer, assume that they either want to see you naked or steal your stuff. Then break eye contact and back away slowly.
Okay, there are a few uses for super strength by itself. Fighting people, for instance, or jobs that require heavy lifting, like construction worker or carney. You could also be a professional athlete, although with all the hubbub about performance enhancing drugs, I don't know if they would allow super powers. And you know that old phrase "you don't know your own strength?" Well, I'm just saying that I hope you don't have anything expensive sitting around your house, because you are probably going to break it.
Seriously? Come on. How many times a day are you fed up with how stupid other people are? Now imagine that you are superhumanly intelligent, and even the smartest person seems like an idiot compared to you. Life would be unlivable.
The only possible answer is to have all of the superpowers at once, Superman style, but even more powerful. Imagine Superman with the additional powers of the Molecule Man, that villain who can control molecules, and so can basically do anything. You could cure cancer. You could solve world hunger. You could stop wars mid-battle. But the thing is, you can't want it. If you want it, you will abuse it. It has to come to you suddenly and without warning, and you have to realize that you were given a gift, and you have to use that gift to help others and not yourself. I know, it sounds a little socialist, but that's the deal.
So if anyone ever asks you what superpower you would pick, you have two choices. You can say omnipotence, or you can say "I don't really want one, but if somehow I was given any sort of superhuman ability I hope I would use it for the greater good." Or you could say "the power to eliminate any smell." That, my friend, would be a useful power.