As a 2nd year resident, NOT at USC or LLU, but rotated there as a med student, LLU to me was better overall. When you are a resident, social issues and patients that don't give a damn if you are helping them was NOT my cup of tea. The residents at USC are way overworked, and if they don't match into cardiology at their home institution, they will have a tough time matching at all.
Think about it. You have Stanford, UCSF, UCLA, UCSD, Cedars-Sinai and possibly Harbor-UCLA that are all better programs than USC and match better than USC in cards. So you are competing against all those other schools that usually want to stay in CA, and cards fellowship PD's will rather take from the higher "ranked" schools than from USC. Also there are ~60 residents you will be competing with, making ~10-15 going into cards...rough percentage.
That being said, LLU, smaller program, takes within, but again, if don't get within program, will have tough time matching into cards anywhere. But overall, better nursing staff, not in a dangerous city, and more appreciative patients.
This is my 2 cents, but if you have received interviews at the above mentioned programs, strongly consider those over USC or LLU, trust me, your cards match will go a lot smoother.