I second what
drizzt3117 said. They are so close academically, it really depends on whether you like the areas around the universities.
I'm a senior at UCLA, so I'm only a little biased here!
I have really enjoyed going to UCLA, both for it's reputation and for the great student life here. Westwood is a pretty cool place with lots of good restaurants and shops, and the occasional movie premiere at the Fox theater. Also, Diddy Riese, which appears to have recession-proof ice cream sandwiches, since there is always a line there. The downside: homeless people who preach, play blues guitar and scream at passers-by. I really can't complain, though. USC kids come driving out of the ghetto in their Mercedes Benz-es to spend time in Westwood, so it must have something going for it. Namely, it's not USC!
The surrounding area is also pretty nice: to the north is a bunch of hoighty-toighty mansions in Bel Air, if you go west you can get to the beach in a short amount of time. Half an hour to the east is Hollywood and points beyond. I'd highly recommend UCLA (again, UCLA senior here). There's tons of research and volunteering opportunities here, too, and a large pre-med contingent, so you wouldn't be alone in your med school quest.
I've heard mixed reviews on Berkeley from friends and friends of friends who went there, thought about transferring, but ended up staying and liking it. But I really don't know what to say, I haven't actually been there myself. Any Bears here to chime in?