I usually debate myself between three particular powers, for various purposes. Though I know I can choose only one, I'll list the three of them, starting with my "first choice" and then continuing on.

This is the power that I truly wish I could have, though I fear I might end up losing sight of my original goals with it.
[hider=Intuitive Self-Flesh Manipulation]The ability to alter my physical body's layout without altering mass. This would be both an activated ability and a passive ability, depending on use. The intuitiveness of the ability is that it fully understands biological processes and materials so that I don't have to when altering my body. It will automatically figure out how to make things work in a natural and healthy way.

Firstly, this ability imitates Accelerated Healing Factors, as it would passively repair any tears in my flesh, re-set bones, etc. Flesh damaged by radiation, acidity, heat, and cold would still be unhealable, however; the best this ability could do would be to expunge the defective flesh and spread my healthy flesh a little thinner to accommodate it. By eating more, I could then slowly regain that lost flesh. This would also allow me to counteract—or speed up—the effects of ageing, rendering me semi-immortal.

Secondly, this would allow me to quickly and easily maintain high levels of fitness, even above that of the most skilled athletes.

Thirdly, this will allow me to take on non-human abilities. Wings? Sure. New senses? Why not. Horns? I guess so.

Fourthly, and this is what really draws me in, it would allow me to take on [i]other[/i] human shapes. I really want to experience being a girl. I like the functionality of the male body and am fully comfortable in it, but there are some peculiarities of my identity that make it so that I would be very unlikely to do certain things unless I had a female body. This would also allow me to take on new identities after this life is over. Once I've imitated ageing to ninety, and all my friends and family's dead, I can just take on a new, young form, and start a new life, and age again. And if my life grows tiring, I could alter my brain to eliminate all memories, and alter my DNA to replicate them at a certain point late in my life.

And every life, I would live new stories, and I could [i]write[/i] new stories. This is more than my superpower wish; this is my ultimate dream.[/hider]

This is the ability that I would choose because it is the least likely to change me at a fundamental level, and is useful while not being obviously superhuman to others.
[hider=Bullet Time]By this, I mean the ability to slow down my perception of time. That is to say, I can think and observe far faster than my environment. This would be a "sustained" style ability; I can activate and deactivate it at will, without needing upkeep.

This ability has a variety of uses, and thankfully, most are internal. When I get writer's block, I could slow down time to help gather my thoughts, allowing me to stop wasting so much of my life sitting around thinking. It would also help to allow me to fully observe the world around me—closely analyse every face on a street, look for a particular item. And as a secondary utility, it would let me move faster.

Note that I do not mean it would give me Celerity; I would still be limited by the limits of my body. But I [i]would[/i] be able to give commands to my body faster, and thus do more complicated motions faster. I could run, write, and do everything faster, though I would of course exhaust my muscles faster as well, and would require a little more sleeping and a lot more eating.[/hider]

This is my "superhero power"; something I'd use if I actually had the intention of fighting evil in a fictional setting. (Note that in reality, I'd choose something far more overpowered, just because I honestly don't want to die. Or more importantly, feel pain.)
[hider=Anchoring]This is the ability to pull things towards you. Similar to Gravity Manipulation, but in which only particular objects are affected, and only particular parts of the body attract at a given moment. This is an "activated" ability; upkeep is required to continue using it.

There are a variety of things this ability can do—many advanced superpowers rely on it in part to function, actually. I could anchor my feet to the ground, becoming an immovable object. I could anchor myself to my opponent, to better grapple or restrain them—anchor my hand over their mouth and nose, and I can kill. Wall-crawling, projectile catching, pulling debris over to use as a shield. I could even anchor myself to a nearby ceiling, and, assuming it can bear my weight, it would pull me up to it to dodge an attack. I could use it simultaneously to anchor myself to the ground and the away from me, in order to pull a building down.

Now of course, some might think that if I anchor two immense weights in opposite directions, I'd jest end up tearing myself apart. [i]However[/i], this power also has defensive capabilities. If I anchor my flesh to the flesh immediately adjacent to it, I can keep my body from being torn apart. Piercing and slashing attacks would be rendering useless, as my flesh would pull itself so tightly together that nothing can go through—though smashing attacks could still damage me, as well as any chemical or energy-based attacks. In this way, by firming my body, I could pull any weight to me, so long as an equally substantial weight is opposite it—though I imagine it would hurt a lot, because even though my flesh wouldn't tear, the flesh is till being pulled, and I would have to put equal power into holding my body together as I would into pulling the object.

This makes for a very versatile power, and a unique superhero.[/hider]

EDIT: Uhhh, I might have broken some rules. I can rewrite it for you if you want, though dumbing things down isn't my specialty.