As an alumnus of Brown, I'm partial to my alma mater. Instead of arguing over which is best, I think it may be better for you to figure out what you're looking to get out of your college education. Then make your decision based on that.

Do some due diligence on the various colleges about majors, financial aid help, post-undergrad resources, extracurriculars, etc.

Good luck!

Dartmouth - good for business-related majors (i.e. Math, Economics, Finance, etc.). I hear a lot of students move on to investment banking and consulting jobs.

Brown - they appear to have a strong Math program that's equal, if not better, to that of Dartmouth's. Also, their social sciences department is reputable.

Cornell - the best of the three for sciences.

Be sure to consider the town you'll be in and the surrounding opportunities. Ithaca is not too far from NY, which is a great place to start your professional life, particularly if you're looking into finance related jobs. Providence is a smaller town, but that may make it a tighter-knit community -- I love getting to know a place really well. If that's someone you enjoy think about that. As for New Hampshire, I hear it's much of the same as Providence. Small town, but great culture. It's also not too far from Canada. Hehe -- road trip!!