I can’t speak to the social aspects, it’s not something I’ve ever really investigated at any schools tbh
However I do want to point out that you shouldn’t necessarily place all your faith in rankings or “tiers” for which school has the better individual programs. But you probably already know that, so I’ll go to my next point.
If you’re planning to go to grad school, and in particular a competitive grad school, your undergrad institution (along with it’s rank or “tier” or whatever) is a relatively small part of your application and a relatively small consideration to adcoms (especially when the difference between rigor/caliber of potential schools is not that earth-shattering, like this case.
What you should really be thinking about if you want to start building up a good grad school application starting now is what you’re going to do in and (especially) outside the classroom with regards to spending time with professors in fofice hours, building up good relations with them (for great recommendation letters), getting involved in out-of-classroom projects (for the experience AND those letters of recommendation), etc. whatever is standard for your major
This is all in addition, of course, to getting stellar grades in all your classes. Once you’ve figured out the kind of things YOU are going to do as an undergrad these next two years to make a great grad school application, then look into each school’s program, research/visit the departments, view course/extracurricular offerings at both universities, and decide which will allow you to your best in (re: excelling academically and doing those extra things that make up the meat of good grad school applications)
I can’t speak to Business-related info on either school so it would be terribly misinformed of me to suggest one over the other, hopefully someone who is into business can come offer some opinion about it. UCs are all, after all, research institutions with a focus on their grad schools and so they (generally) are known for doing a pretty good job in preparing you for grad school, perhaps SDSU has a similar reputation but tbh I haven’t heard much about it.
UCSC is the most beautiful place I can imagine living an going to school on the other hand (although careful if you have strong allergies lol) and idk about SDSU. I would of course encourage you to visit both campuses as well. Feel free to PM me for anything Hope I helped a bit, and congratulations on being admitted to both schools!