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.