There are obviously pros and cons to both choices. I think at Chicago, you will be surrounded by a much more intensive and rigorous intellectual community. Plus, you'll get a "campus life" in a way that you won't with the New School. However, if you like a more integrated urban existence and think you'd love spending your next year or two in lower Manhattan (with all of the benefits and challenges that brings-- including commuting, if you're not lucky enough to get subsidized housing on campus), then maybe that's the best choice for you. I don't know your particular field, and that matters a huge amount too, as does the reputation of the program, and the faculty. Is your goal to continue on to a PhD program? If so, your most important concern should be with faculty. Work with well respected faculty whose research jives with yours and who you actually like on a personal level (to that end, visiting the schools and departments would be a good idea, if you haven't already). If you're not looking to continue on to a PhD program, then the reputation and quality of the faculty is less important. Chicago certainly has a more prestigious name, so there's that to keep in mind, but the NS has a reputation for cutting-edge work. The last thing I would add is that the NS has a HORRIBLE reputation for the way it treats graduate students. It's literally considered one of the most hostile environments in which to be a grad student. If you were doing a PhD, I would advise against the New School for this reason, but if it's just an MA then you're not in for the long haul and that could be less of a concern.
Obviously, no easy answer! The best bet is to think all the pros and cons through rationally (maybe make a table), visit, and then listen to your gut feeling.