I'm currently a graduate student in Biochemisty at a UC as well as completed my undergrad at a UC. The prestige and name does carry a bit of weight. My bias towards a UC is obvious, but if you want to at least do research in your undergrad, I would definitely go to a UC. There are many outstanding professors with a great personalities that you can work for that are at the forefront of their field, however there are the exceptions. Many of which will support you, and help you realize your goal. (if you work for some professors that are on the admissions for the med school, they might actually help you get in at that med school.)
I never really cared about the huge class sizes. I don't see a difference once it reaches anything above 40, except trying to diffuse in/out of the class when class starts/ends. If you need help. there is always office hours for the professors, and many ta's, that are barely used at all except during those few times of the quarter. Once you get into your upper division classes, if your so concerned about class size, it drops quite significantly. I've had classes from 8 people for upperdivision classes, to around 120.
The "college experience", i'm assuming your in your late teens/early 20's, is something you definitely want. Attending the large concerts, on your choice of poison or lack of one, going to the games, or participating in the traditions, shouldn't be simply thrown out. This should be in my opinion, a large factor in your choice. Where else do the Grad students keep alcohol in lab, and have initiation drinks with everyone(professor may be included)... - lets ignore everything wrong with this. You definitely want your last years as an undergrad to be a fun one, you're giving up quite a bit of your life after that.
There is a lot of talk about the competiveness that comes with the UC. It's true, but most professors don't like failing students. There is quite a bit of grade inflation at the UC's, and as long as you put in the time and effort into your classes you will do fine - You earn the amount of work you put in. I don't like hearing that statement about competing with those who are cut throat and because of that, due to the curve, its harder for you to earn your grade - It just gives me a bad taste in my mouth as it screams you would rather compete with mediocrity. Think of it as a slight taste of what it would be in med school, as it would in my mind be much worse. Just worry about yourself, and not others. Berkeley might be different, but they're just crazy over there... kidding
Anyways, just remember though a 3.8 from a cal state would look better than a 3.0 from a UC, but how it would compare with a 3.4 from a UC I would think seem slightly more equalized - no matter how wrong this is.