You will get a good education at all the UC’s including UC Merced, Riverside and Santa Cruz.
Weather: Riverside is inland so you will have hot weather in the summer and mild temperatures in the winter. Nothing too different than any inland suburb in Southern California.
Santa Cruz is near the Northern California coast and has a lush forest-like campus. Summer temperatures are mild and cooler than inland campuses. Winters can be cold and wet. Due to being near the coast, you can have the foggy/gloomy mornings which are similar to the Long Beach area.
Academics: Both campuses have a comprehensive Biological sciences program.
I suggest you look over the curriculum for each school below:
https://cnasstudent.ucr.edu/biology#additional_documents
http://cnasstudent.ucr.acsitefactory.com/sites/g/files/rcwecm2691/files/2019-07/biol_bs_4yrcourseplan_fall18.pdf
https://mcd.ucsc.edu/academics/undergraduate/advising/academic-planning1/hbio-frosh-plans.html
Social scene: You can find a party at any school and the social scene will be up to you. If you live on campus, there are many options for students that want good social interaction but also want to be serious students. I would encourage you visit each campus, talk to students if possible to form your own opinion.
Dorms/Quality: Plenty of websites such as Reddit and Niche to get opinions on dorms. Again, once things settle down, I suggest you visit if possible.
Types of people: All UC’s have diverse student populations but you can look at the demographics each campus here:
https://ir.ucr.edu/stats/enroll/demographic
https://admissions.ucsc.edu/why-ucsc/facts.html
Over the years there have many stereotypical ideas of the type of students that attend these campuses. The best way to find out if either campus is of interest is to do your research and visit.
As a parent whom visited all but one UC campus, I found something to like at every campus and found each unique but it is up to you to decide which would fit you best academically, socially and financially.
Personally, apply to both and see where you are accepted. No extra work for the UC application other than an extra $70 application fee.