As a product of the CSU system after transferring from a CC, I would have to say CSU is better for a few reasons.
1. CSU is much cheaper than UC, by around 50%. You are already going to be blowing through cash going to medical school-don't add an expensive undergrad on top of that.
2. CSU's have smaller class sizes and the professors are much more accessible. This is extremely important for LOR's.
3. Many UC's grade on a curve that destroys GPA's of undergrads. CSU's are more forgiving.
4. CSU's have plenty of research opportunities, especially the one I went to.
PM me and I can tell you a lot more about the advantages of CSU over UC. The one I went to is especially good at getting pre-meds into good medical schools.
As a current UC student that transferred from a CC, I'll share my own opinions.
1) No disagreement here, though both are significantly cheaper than most private schools.
2) I have experienced a number of large classes at my UC, and it is certainly difficult to get to know the professors teaching them. That being said, UCs offer plenty of smaller classes as well. I don't think you'll have a problem getting LORs from excellent professors as long as you show genuine interest in the courses, even if they're big lecture halls.
3) It's true that many of the classes are curved, but that shouldn't scare you away. The curve will only destroy you if you're an average or below average student, and there's really no reason for you to fall into that category if you're serious about going to medical school. The curve should only help you as long as you have a very strong work ethic and properly prepare for all of your courses.
4) I can't speak for CSU research opportunities, but there's certainly plenty at all the UCs. I was accepted into an amazing research laboratory at the beginning of my first quarter at my UC.
Both CSUs and UCs should provide you with plenty of opportunities to become an excellent medical school applicant. I'd recommend the UC route, but I haven't experienced a CSU and I'm obviously biased. Feel free to PM me if you have any specific questions and I'd be happy to answer them as best as I can.