What I "would" be is Cubone, according to some internet test. That was a while ago, though, and I've changed since then. So I doubt it would be the same still.
I probably would want to be something like a Rattata. Seems fun to me.
In the long run, though, something more like Liepard would probably be better. Still very agile, so I would be able to get around quickly, but not as weak as Rattata.
If the idea is just to have fun and rampage, though, then Charizard. [: