Well... I plan on applying to both of these schools next year, so here's my opinion.
You can't go wrong with either school. I would most likely choose UCSB, because I loved UCSB's chill atmosphere, and the fact that everyone loves Gaucho Soccer (National Champs)!!
But I love Pepperdine too. I think the school offers plenty of social opportunities (and this is coming from someone who is applying to Miami, SDSU, and ASU). First of all there is the beach. And about 25% of the student body is greek. Also Santa Monica, Westwood, Beverly Hills, and Hollywood are all just a short drive away. Also Pepperdine has some pretty awesome sports teams.
Good luck with your decision.