As to your pros/cons: https://www.aamc.org/download/462316/data/mcatguide.pdf
see p 14.
As to prestige difference: where you go to school is of lowest importance to adcoms. Both schools can be pathway to med school. Whether you are successful will be more related to your efforts, less on where you attend as between these two schools.
As to ECs: Not sure your definition of “quality” ECs, but adcoms expect to see you have some idea you know what you getting into as a future MD. Clinical volunteering is of highest importance to adcoms as an EC. Both schools/ locations will offer you the opportunities to participate in meaning ECs that adcoms expect to see. Again whether you get involved will be more due to your efforts, less on where you attend as between these two schools.
Research is not a must EC and will be quite unimpressive if your time in a research lab involves say cleaning glassware for grad students. A problem with research activities is if your plan is to graduate then immediately start med school is that you must submit a complete application in summer after junior year. It will be hard to be involved in meaningful research activities (eg published) by end of junior year. If you’re dead set on career in research and a med school big on research, you may have to consider taking a gap year(s) and being involved in some meaningful research activity, UCB might be better option.
All US med schools are good schools and can serve as pathway to whatever area of medicine you are interested in. Most successful students who gain admission to med school only get one acceptance anywhere. And as a California resident, understand, it’s much more likely than not, if you get an acceptance, it will be OOS…
I’d rephrase that and say most who start as premed change their mind and never apply, and of those that do apply, approx. 60% will not start at any US MD school. Putting aside premed, consider what’s your academic attraction as to either school. What academics are offered at either school that can serve as your plan B or C should you change your mind.