I'm a graduating senior from UCSD, so you can take what I say with whatever bias you think is appropriate. The school is beautiful. Everyday is like living in a paradise, weather and setting wise. The school is challenging. It is a research institution and research is its primary goal, be it clinical or basic. This does breed compeition and that competition does filter down to the students, at least at the undergraduate level. Some of the faculty are good teachers and some aren't, but most are great researchers. The clinical experience, from what I've seen of the patient population, is amazingly diverse in San Diego, although the campus itself is not diverse. I'd go so far as to say that UCSD is the least diverse of the UC campuses, but I have nothing to back that up with, just an observation.
If I was in your situtation though, which I'm not as I was rejected from OHSU and am removing myself from the waitlist at UCSD, I'd pick UCSD. I never regretted going there for undergrad and wouldn't mind staying, although I definitely am pleased that UCI appears to be a less overtly competitive environment. OHSU seemed a nice environment as well, but going down to the river...just doesn't compare to the beach.