The fact that you're even considering grad school is huge. Be proud of that.
I toured both for my PhD apps. UCSC felt like home immediately—the redwoods, the ocean, the laid-back students. But my mentor pointed out something important: "vibe" doesn't pay rent. Look at stipend offers. Look at health insurance. Look at guaranteed housing (UCSC's is limited). UCR offered me more money and actual housing. That practical stuff matters for first-gen students without family safety nets.
Also consider your support systems. Does one school have a first-gen grad student group? Does one have better mental health resources? These things matter more than you think.
Visit both. Talk to current grad students (not just faculty). Ask about their actual lives, not just their research. You'll find your place.