The OP’s question is more difficult than its surface appears (UCLA= much more prestigious, so go to UCLA!). For pre-med, Santa Clara might be much more useful for the OP. Pre-med is brutal, but if the classes at Santa Clara will allow the OP to have more guided help from caring professors, enjoy a less competitive environment, and avoid intentional weeding-out classes, then this might provide the OP with a stronger chance at medical school.
Weeding-our courses are very real, especially at an elite school like UCLA, where hundreds (maybe a thousand?) undergrads arrive with plans to go to med school. If this is not the case (or not so much the case) at Santa Clara, a Jesuit school of 5,500 undergrads, maybe SC is the smarter play.
But as I always say, the ground is littered with the bones of once-hopeful pre-meds. Back in the day, one friend of mine switched to law school. Another switched to dental school. Thus, the OP should think about which school will help her/him in the long run in case med school is not an option. The OP should also think about which school, in general, will make her/him happier. In CA, both schools are well-known, so it’s not as crazy as some would think to not go to UCLA, although, yes, UCLA is a highly, highly selective (did I say “highly”?) university.