Okay here is my .02 but be warned, I am extremely biased!!!
UCLA is much better than UCSD because it has a top notch reputation, best hospital in the west, inexpensive (for cali residents), pass/no pass, and the atmosphere at UCLA is incredibly relaxed. Rumors of UCSDs intense nature are somewhat true--you will definitely be working much harder than your friends at other schools. UCLA students rock the USMLE and have a distinct advantage at UCLA residency programs. If you want to work in Cali in the future, an MD from UCLA will take you very far. Westwood is the quintessential college town with stores/restaurants open late and a good variety of food at decent prices.
UCLA is WAY better than UCI. UCI is a good school, but it is way behind the other UC schools as far as repuation/matches. Irvine is a *nice* and safe city, but there isn't much of a nightlife.
CRIBS: UCLA is expensive, as is most other cities, but you can find a nice place for $800/mo in Santa Monica. Housing at UCSD and UCI are on par as far as prices are concerned but are probably better quaity since those areas are "newer".
GRINDS: UCLA - sorry can't beat LA food.
CRASHES: UCLA - Sunset Blvd.