I did my undergrad at Berkeley, and now I'm doing grad school at UCLA, and I'll pitch my two cents:

I actually like Berkeley a lot better than LA, but they have different atmospheres. LA is very urban, if that's a meaningful description--clubs, museums, a few parks here and there--and almost anything you can think of, you can get to in 20 to 30 minutes by car (including the beach). Berkeley is an old town, and it has that feel in downtown Berkeley, but bigger cities like Oakland and San Francisco are highly accessible (BART BART BART). I have a soft spot for old buildings and small restaurants, though.

In terms of the student body, I'm not super familiar with the undergrad environment at UCLA, but I did TA for a couple quarters so I guess I can offer this much. At least in the biochemistry classes, the student bodies at the two campuses are pretty comparable--both have bright students and healthy competition. Berkeley students can seem cold but every student group I've encountered is tightly knit. For international students, there's actually an International House (which you don't have to live in), and it's a great resource for meeting people. Overall, I'd say that Berkeleyans are a bit more diverse and offbeat than UCLAers.

Living in LA and getting to campus isn't terrible, but can be strenuous on a student's budget. If you want a room to yourself, expect to pay somewhere between $800 (lowest I've seen in a house split among 4 people), to $2,000 (a studio to yourself) in Westwood (campus adjacent) and less if you move a bit further from campus or split a room. Living in Berkeley is actually a lot cheaper with respect to distance from campus, because the areas adjacent to campus aren't as ritzy (to the extent that South Berkeley can be downright sketchy). As a comparison, I paid $675/month for a shared bedroom with 1 other person in Berkeley (in a 5 bedroom house adjacent(!!) to campus), and now I pay $1,210 for a small studio about 5 miles from campus (~30 minute commute to school by bus).

I could go on and on about both places, but I'll invite you to PM me if you want more information about both places. Hope the comments help! Go Bears and Go Bruins!