despite all the claims that UCLA is harder to get into than UCB, UCB is undoubtedly the toughest to get in of all the UC's.
UCB has a better academic reputation than UCLA does, although as many mentioned it depends on your major. I'm majoring in Philosophy and UCLA's Philosophy department is one of the best in the country. Premed at UCLA is also very well regarded, and it just so happens I'm a premed also hehehe. Other than that, UCB is better at almost everything, but not by much. It's mostly reputation, and we all know how empty reputations can be. In any school you will get quality professors, it's just a matter of how your employer/grad school/prof. school will be disposed to value your resume.
On the other hand, UCB is a dump. They have a lot of trees everywhere, but I think it's to cover up all the garbage, and so that people can hide and light a spliff on campus. Right outside campus you have a lot of crazy people and drug dealers and the people in campus are pretty crazy themselves. It will be cloudy a lot of the time too, which can get kinda depressing.
UCLA is right next to Bel Air, in the city of Westwood. People are pretty much normal, if not TOO normal. But the cliches are true... you will see everyone on a cell phone with sunglasses and sandals. If had to choose I would pick UCLA in a heartbeat. I haven't always felt that way but the longer I'm here the more I'm glad I chose UCLA.
I don't know much about UCSD but I hear they have an awesome Bio and Marine Bio department.
If you like to party like crazy then UCSB is the best choice.
If you like cows then Davis or Riverside will suit you well.