I am also someone who is set on law school so I am also pretty "in-tune" with how that works and I think I can offer a different perspective. - Law schools are going to care little about the difference between Duke and USC. If it were Duke and a no-name state college, that would be different, but, even then, GPA and LSAT score DOMINATE law school admissions and where you go isn't a huge factor.
With that being said, you can't go wrong with either and, to be frank, with a choice this close you will probably always have a lingering "what if" feeling whenever you do choose. But, at the end of the day, do you feel more like a Trojan, or a Blue Devil?