CC vs UC Summer Sessions?

I’m a junior in a Californian high school, and I’ve decided on taking college classes over the summer to strengthen my applications by showing I can handle rigorous coursework and getting letters of recommendation from my professors. I want to go to a UC for engineering after graduating high school.
Now, during the summer between junior and senior year, would it be more beneficial to attend a local community college, which could be cheaper and allow for time for more activities during summer, or take courses with the summer session of the UC’s I would like to attend, which, despite being more expensive, may strengthen my application? I can pay for either and have no prior commitments and I’d greatly appreciate it if someone could weigh in on pros and cons regarding cc courses vs summer sessions.

If money is not a factor I would do the UC summer programs. They are taught by very knowledgeable professors and/or graduate students and you can “test drive” the college to see which one you might want to apply to as a senior. You also can live on campus which is an experience all to itself.