I went from a BS and MS at UIUC to UCSB.
When I went to interview with the UCSB research group, I was a little lost. I asked someone where the EE building was, and they said it was on the fifth floor. One floor?!?!? It really wasn't as bad as that, though, and the engineering campus has grown a lot in the past five years.
I was offered a position at UCSD, and I took UCSB for the better (arguably the best) semiconductor research. UCSD's semiconductor days are (sadly) gone, but the profs are still there.
As an undergrad, I'd probably go with UCSD because it's a larger school, it'll have more resources, more course selection, etc. I mean, UCSB has EE, ChemE, MechE, CompE, MatSE, and what else... do CS, physics and chem count? I audited undergrad EE classes at UCSB. It wasn't all that tough. Lots of whining, and lots of profs giving into students demands rather than failing them. It was weird.
I'd go with the bigger school if you're going for the undergrad education.
If you're going for the lifestyle and chicks, you should at least visit UCSB!
BTW - I wouldn't say chicks are walking around in bikinis at UCSB, but you get sunbathers in the common areas... I don't think it's any different from a lot of other campus quads and stuff.
My old roommate and my squeeze are both still at UCSB. They (independently) told me there are tons of Japanese girls on campus this year. They're not sure why.