Its a very easy choice. I am a big fan of USC, but if I had to choose between UCLA and USC, I'd take UCLA anyday. A friend of mine goes to USC, and she's going to graduate with $200k in debt. That's simply not possible at UCLA, considering the cost of attending is $20k less per year. Besides, UCLA is very well known for its outstanding research, while USC is not.
One caveat: If you wish to go into ER med, IM, or other clinically intensive specialties, USC might be the better bet with LA County at your disposal. You'll see anything and everything at County. County is amazing, and offers clinical exposure second to none (ok, maybe second to Bellevue.)
Edit Note: County was the last hospital in the US to see a case of Leprosy. Think you'll see that in Santa Monica?