I faced a similar decision 4 years ago, deciding between UCSB, UCSD, and USC. You can't go wrong with either Santa Barbara or San Diego-- both are good schools with beautiful surroundings, etc. but San Diego is definately regarded as a "harder/better" school.
You seem to be asking if law school admissions committees will know the difference between the two schools, correct? In my opinion the difference between a degree from UCSD and UCSB is negligable as long as you do well (i.e. a 3.7 from UCSB will likely look a lot better than a 3.5 from UCSD). But, are you certain that you will go to law school? I started college as an Economics major. After one semester I switched to Marketing, and a year later I switched to Political Science and decided on law school.
You may realize that you have no interest in law school after taking a few law related courses. Or, you may bomb the LSAT and decide to pursue other options. If you are not dead set on law school and sure that you will go, you should look into the non-law related career prospects from each school (I would guess that UCSD's are better). That could factor into your decision.
Overall, I would recommend visiting both (if you haven't already) and then going with your gut. If you feel you will be happier/more successful at UCSB then go there. If you think that you may end up in a field other than law and are worried about "cutting yourself short in the future" then UCSD may be the best option. But as far as admissions to law school goes, all other things equal (LSAT, extra curriculars, work experience, etc), the difference between the two will not be a significant factor.
(for the record I chose USC, so I am neutral)