Human brain, with ability to climb anything I wanted and be able to go naked without scaring half the world? Woohoo! Not to mention that chimp don't really have to DO anything if they can stay away from captivity. But since I would have the brain of a human, I could figure out how. (one hopes.)
I chose to have the brain of a chimp. Here's why. I would never have to deal with this whole being responsible crap ever again. People would treat me like crap, but hey, I'm a fricken monkey. I don't care! I'd be driven by instinct back into the jungles and forest where I could like a happy simple monkey life.
The other way around, I'd feel the need to be loved on a deeper level, to communicate, to be intimate, but I'd never be able to with the body of a chimp. Ignorance is bliss.