Congratulations on all your updates! I think the fact that you’re so a great teacher (to debate team members and to others on the track team) is awesome! I would see if one or both of your letters of recommendation can highlight that as well. It’s a really great way of showing how you contribute to your community (showing vs. telling).
With respect to Cal vs. Cal State, it probably doesn’t make a world of difference, but I would probably go with the Cal State option. Why? First off, you prefer in-person interactions. Secondly, you can learn (and universities know you are learning) about higher education research and how it is done. Additionally, the professor can indicate the real added-value of having you on the research team. This is important because there are students who post on these threads and talk about all their research with professors but it seems…dubious, particularly when other threads show websites where families pay a certain amount of money and their kid gets involved in research and named on a research paper. Not to say that none of it is legit…but this opportunity you’re talking about makes a lot of sense to me as an outsider. Thus, I suspect it will make a lot of sense and seem more legit for an admissions officer, too.
Be that as it may, I don’t think you’d go wrong with the UC professor. I am just putting in my two cents for Cal State. People in academia realize how challenging it is to get full-time positions at any college, regardless of its ranking on USNWR. I don’t think the university affiliation of the professor you’re being supervised by/doing research with will make much of an impact.