Lets suppose you could have irl a superpower. However the rule stands it can only be 1.
this means you can't have multiple powers like certain superheroes do, seen as how they have additional powers to protect them from the rigors of said super powers.
Infact lets make a game of it. I'll think of a power to have, say why i think it would be great to have, and the next person writes a reason why that power would suck and the problems it would cause, then for them to suggest a power they'd like and why it be great and so on.
Power of regeneration, able to heal from any wound or disease and remain healthy because of it.
This would be great because I'd never have to worry about ever getting sick, could heal from any injury so able to push myself harder, and in general would live a long healthy life.