Hey, congrats on your acceptance to two great schools!
Background: I’m a sophomore at UCSD, and if you are still looking for input on UCSD for making your decision, or maybe someone else is reading, here are my two cents.
UCSD is socially dead in the sense that the party scene (which I don’t have much knowledge about-- because I’m not interested in it) isn’t that prominent, because you need to look for it, as it is not out in the open. Our Greek life, sports spirit… or school spirit for that matter, these definitely cannot compare with UCLA. If those things are must-haves for you, UCLA may be better.
But as for more laid back, smaller social gatherings, they are definitely out there. We’re all college students, and it’s not like we do nothing but study! There are many student orgs, and friend groups that readily form, with so many students looking for new friends as they enter college. They are all in the same position as you, after all.
Unless you stay in your room all day, complaining on Reddit how UCSD is Socially Dead, you’ll likely find a niche in terms of your friend group. I would say, however, that living in the residential halls rather than an apartment (or living off campus) freshman year makes meeting new people easier.
As an example of what my social life has been like, some of my friends did this for April Fools last year: (I can’t post links but they put eyes on the library basically)
Attending hackathons with them, and suffering through classes together really bonds us together, even if we’re in different majors/colleges.
I’m also involved with a faith org on campus, and it’s really great to have a community of like-minded people away from home. I’m actually living with them this year (well, until Coronavirus hit…), and it’s been a great experience.
…I realize I might sound a little too enthusiastic about my school, but hopefully some of it helps you with your decision. It’s a little late and I might be rambling way too much ahaha.
I’ll close by saying I don’t think you can go wrong with either choice (however cliche that might be), because really, both are great options. Congrats again!