It’s hard to compare UCSD and UCI academically because (I’m guessing) most of us haven’t been students at both places. It’s all going to be conjecture really.
I can say that UCSD is a great place for pre-meds. I was a biochem/bio major so I can’t speak for the chemistry program, but the biology program was great. I really liked all of my professors, and there’s a lot of great classes with a medical focus (in the biology department but also in other departments, like psychology, sociology, urban studies and planning, etc), which is nice for students interested in health and medicine. I didn’t go to medical school, but I did feel like UCSD prepared me really well for graduate school.
There are a lot of pre-med students so there are a lot of resources for students in terms of infomation about applying and pre-med orgs to help you get involved.
Something to keep in mind is that the medical center at UCI is about a 30 minute drive from the main campus (there’s a shuttle, but it doesn’t come very frequently). I didn’t have a car at UCSD but the hospitals and medical centers were all much more accessible at UCSD than at UCI (I worked at the UCI medical center, so that’s from experience).
Also, there’s a lot of research opportunities at UCSD on campus, but there are also a lot of nearby places to do research. Salk and Scripps (both well known research centers) are literally across the street from UCSD and it’s fairly easy for students to volunteer or work there. I also knew students who worked at labs nearby. I don’t know how many research centers or labs are near UCI’s campus.
Also, in my opinion, there’s not that big of a difference between 1.5 hours and 3 hours, but I also was a 7 hour drive from home when I went to school. It’s close enough that you can still go home when you want, but you likely won’t be going home that often. I knew lots of people from LA that went to UCSD and none of them had problems getting home whenever they wanted. Some took the train, some drove, some carpooled. It’s really not that far in the grand scheme of things so I wouldn’t weigh that too heavily. It’s good to live a littler further away from home sometimes. It forces you to figure out things for yourself a little more.