I go to Caltech for graduate school and lived in Northern California recently. Caltech is a very unique place. Have you visited? It's very small and has it's own unique atmosphere. The students here are definitely more nerdy and science-y than in other places. It's also important to note that Caltech does not have a medical school which is quite different from UCSF in that regard. There are only a total of 2000 students here. Also whereas UCSF and Columbia are in the city, Caltech is definitely in a more suburban environment. That said I really do like Caltech. The people here are really, really smart and people are really friendly for the most part (if sometimes not that socially adept). Pasadena is close enough to LA that you can go there for dinner or go to a club.