The biggest difference is RISD's foundation program, which is essentially boot camp for artists, based on the traditional Bauhaus teaching method. As an old school RISD grad, I strongly believe in this as the basis for all creative professions.

The head of Architecture at Harvard is an unlicensed RISD grad.

USC is very respected in Los Angeles and has historically produced the majority of Southern California's architects.  It will be more expensive to live there, and it's not in a great neighborhood though there is safety in numbers and it's a well-secured campus, but L.A. is a phenomenal architectural laboratory, with its own architectural legacy, and a great place to be when you're taking a break from architecture to take part in an infinite number of recreational, cultural, and entertainment venues.  Again, it depends on where you want to be - do you want to work in LA or NYC when it's all said and done?

Parenthetically, that's why you have so many "screwed up" people in LA with roots in both NYC and LA. They love LA for the weather, the geophysical and recreational amenities, the lower density, and the pushing of the envelope while they love NY for the culture, directness, higher "world city" status and importance, and cheeky, more tolerant multicultural fabric.  It's quite a conundrum to pick between these 2 places.