These are some fantastic answers: some are insightful, some are clever, and some are downright hilarious xD .
For those wondering at the logic of the scenario, the question presupposes that there are or can be gods, so the God of Gods up there would indeed get to be the Top God if that's their bag. How they remain Top God is a story waiting to be told.
And one need not worry about screwing things up; it is the folly of man to try to play god, but it is the privilege of gods to screw things up for man. Divine Right and all that >_< .
As for me, while there's another god I'd likely be due to my personality, I would wish to be the God of Wisdom. I would be a quiet and reclusive deity who spends nearly all his time beneath a tree atop a verdant hill. The tree would be populated by many types of birds, and they'd chirp a mystical tune. I'd just sit there meditating, smoking an herb of some sort, and watching the stories of the world unfold through a big ol' mirror or somesuch.
I'd share my gift through conversation, but people would have to find me first and actually sit with me to receive it. It could take hours, it could take years, but if they made a genuine effort to have a real dialogue with me, I'd never fail to lead them to wisdom that could change their lives, and maybe even the world, for the better.
Oh, and I'd also be completely invulnerable, of course; I imagine some people would try to beat on me if they didn't like what I had to say x) .