haven't been to usc yet, but tufts and nyu were good schools i think. i would personally pick tufts over nyu, just because i like the location in boston a little more, and tufts is a little smaller, so more managable. nyu gets a bad rep on this forum, but it was a solid school in my opinion. nyu, imo, had more opportunities and if you're the type of person that takes initiative and opportunities, i feel like nyu would be a good choice.
tufts has a much better name, and in boston and the new england area, tufts is the school with the best reputation in terms of clinical exposure. good opportunities as well in research, but i didnt see the facilities. the research facilities at nyu were phenomenal. tough choice between the two i think. i think it would basically come down to which city you'd prefer to live in as long as you don't mind the larger class sizes.
usc also gets a really bad rep on this forum. to go to usc, you really need to take initiative and be comfortable working on your own. the atmosphere at usc is my favorite though. i love being on the undergrad campus, and love usc sports (i go to all the usc football games). i really don't know much about their program at this point in terms of research and such, but i have many friends that go there, and are happy. they end up having a lot of free time, but you have to be on top of it, and use that free time wisely. also like others said, LA is as cool as NYC or Boston, but you are close to the beach, and the weather is always great.
basically, each school has it's positives and negatives. all are expensive, so that shouldn't be too big of a deciding factor. it comes down to personal preference as one school is not better than the other, just different. try to choose the school that you're happiest with, and the area that you'd be most comfortable.
hope i didn't confuse you more.