Should I stay at UCM or should I transfer where I got into?

Hello all,
I am currently a first-year UCM student who was successfully able to do a UC-UC transfer and was accepted into UCSB, UCI, and UCR. As a student wants to go to grad school, would it be in my best interest to stay at UC Merced and get a higher GPA while being more likely to do research, or would it be foolish to deny the schools?
Also, I’m not exactly sure which school I would choose. I was accepted as a Chemistry major for UCSB, but as Pre-Chem for the other two and I’m not sure that I want to do chemistry anymore. I was planning to switch into Biology or BioEngineering and I don’t know which school is best for that. I also enjoy the small campus feel and just the overall feeling of unity between the students on campus. I am not into the party scene very much but I do enjoy being able to go out and find distraction or things to do on occasion.

I’m not sure you can transfer into bio or engineering. I don’t know the rules for all the UCs but those majors are often blocked. If you’re happy at UCM and your plan now is to switch, I’d stay at UCM.