While a mid-point location looks seductively handy for this, I'd really recommend that you consider three different hotels so you can spend more time taking the pulse of the very different communities involved. USC and Los Angeles is a mix of very "urban gritty" with "pockets of sophistication." Pepperdine & Malibu is much more rural than you'd imagine that close to LA and the beach. And Santa Barbara is it's own special vibe of a Mediterranean clime with California cool, with Isla Vista a funky mix of college town and surf camp.

I'll admit, I'm prejudiced in favor of UCSB, having just finished my PhD from there this June... And for undergrads, it's tough knock a campus surrounded on two sides by the Pacific Ocean where you can study on the beach. Can I ask what your boy is looking to study? (PM me) I might know specific folks on each campus for him to talk to to get a better feel for their pros/cons...