Yale is pretty much my favorite campus anywhere, but unless you really, really, really, really love Yale more than USC, I’d take the full ride and go to USC. (I actually did go to USC.) Where you go to law school is going to matter a lot more than where you went to undergrad.
USC specifically targets scholarship money to steal students like you away from places like Yale, so you can be sure that USC really does want you. And it’s always nice to feel wanted.