What do you want to do during and after college?
Personally, based on your 3 criteria, I feel UCSD is the best choice. It has a much bettter chemistry program than the other two, you have 3 (or 4? I forget exactly) of the largest research institutions in the nation nearby, including UCSD itself, and, despitewhat everyone says, it actually has a social scene. It's nowhere near the caliber of UCSB's, but it exists if you're willing to find it.