Hi, @adaserk -
My D was also admitted to the UDub as well as Scripps. And in terms of the setting, she loves Seattle and is not a big fan of SoCal. She LOVED UDub when we toured, and I think if she had gotten into Honors, we would still be debating. But UW Honors turned her down, whereas Scripps offered her enough merit to make the 5C’s actually *cheaper" than UW OOS, despite the Purple & Gold thing. And the majors that interest her at UW have a 30% admit rate or less, and she didn’t get direct-admit. So… UW pretty much took itself off the table. I totally understand the appeal of UW, though, and get why you’d be conflicted.
There is no contest in terms of the faculty attention and mentoring that you’d get at Scripps vs. UW. (Can’t really speak to UPS and Seattle U.) It’s a little better if you have Honors at UW, but still, a lot of your classes would be outside Honors. There’s a lot of competition for resources there. In many ways it serves grad students better than undergrads, though of course for the right student, it can be a terrific undergrad experience. It just takes a lot of hustle to make it terrific. Depends somewhat on your field of study, though.
Size-wise, I think the small school within the larger consortium at the 5C’s seems very best-of-both-worlds. (Scripps would be too small as a stand-alone, at least for my D.) But Seattle U is nearly as big as the combined 5C’s, and UPS is is a decent middle ground size-wise.
My D shares your dubiousness about the LA climate and vibe. I do think the Scripps campus, though, does a good job of providing shade and water features that mitigate that “bug-under-a-magnifying-glass” feeling of overwhelming sun, lol. And the fact that it’s on the edge of the LA sprawl feels more psychically comfortable than being surrounded by sprawl on all sides.
I would think that a lot of it would come down to your specific academic and extracurricular interests, and where you see yourself having access to the opportunities that fit you best. Plus, of course, the intangibles of “vibe,” and the all-too-tangibles of cost.
It sounds like you need a more systematic decision tree. My though would be… first decide which you would choose if you had to pick a WA private U - i.e. look at the UPS vs. Seattle U decision, pick one and take the other out of the mix. Then look at each of the remaining three pairs and decide which wins. Hopefully this won’t leave you with a “rock-paper-scissors” loop, but rather a clear winner. 
Not sure if any of that helps, but I look forward to hearing what you decide!