Tim,
As a native Californian, I'll throw you my $.02. Here's my take on the major cities.
SF: Only city in CA that even comes close to East coast city life. Unfortunately, living downtown means paying $bank$ for rent. Alternatives in the bay area are downtown Oakland (by Chinatown, they've really cleaned it up over the last few years) and Berkeley (which has great atmosphere but is fairly suburban).
LA: My hometown, I love it, but doubt I would if I hadn't grown up there. Basically, most of its suburban sprawl; mini-malls and tract housing and over-developed desert. However, there are a few select locations that are incredible. Westwood (UCLA) is fantastic, you can actually WALK places. Santa Monica has incredible beaches, and the area by the SM airport is pretty cheap (tho it's not on the beach). Redondo Beach, Manhattan Beach, Hermosa Beach are awesome and have great little 'downtowns'. East-Los, by USC, is a complete hole. If you move there plan on getting your car stolen.
Irvine (~50 miles south of LA): It's okay. Plan on getting a Honda/Acura and lowering it (I did
) I did my undergrad there, so I'm well-versed in the evils of Orange County. If you choose UCI, live in Newport Beach, preferably on the penninsula. Its a 15 minute drive from the campus (along PCH), but it has INCREDIBLE beaches. Because a lot of students/surfers live on the penninsula, its still relatively cheap too. Irvine's full of overpriced, cheaply built apartments and condos...Everything looks the same, so to me its basically suburban hell (but a great place to raise a family).
SD: Great city, much more mellow than LA. Again, if you're looking for big-city life, you won't find it here. Things are pretty spread out and laid back. La Jolla (UCSD) is the Beverly Hills of SD; it's beautiful but snobby. You can live cheaper in Miramar (with all the military families) or in Pacific Beach (with all the surfers). I'd choose PB...great bars, great beaches.
Davis: Lots of cows. Close to Tahoe. That's about all I know.
Anyways, hope this helps. Email me if you want further info.
-d
PCOM, Class of 2005