Competely depends. Do you mean in the pokemon world, or in the real world? Because honestly, if word got out that you, a human being, could perform ANY of a majority of pokemon moves (Transform, Psychic, Heat Wave, Rain Dance), you would be hounded for documentaries, scientific studies, government surveillance, and probably get death threats. :( And what point would there be in being able to breath fire or shoot lightning, if the only time you'd be able to use those is when fighting crime?
If I was a human in the pokemon world, I would want Tri Attack. With proper training, I might be able to land the proper effect when I need to. It's essentially 3 attacks for the price of one. :)
Or no wait. Maybe Heart Swap. You can force people to temporarily switch bodies. That would be... chaotic. >:)