Does UChicago or MIT offer more merit aid for undergraduates?

The biggest practical tradeoff is that MIT does not award merit scholarships at all, while UChicago does offer merit-based scholarships to some undergraduates. That means if “substantial merit aid” is a key part of your comparison, UChicago is the only one of these two where that is realistically on the table. MIT’s undergraduate aid is need-based, and the Institute is very explicit that it does not use merit awards in its own financial aid program.

At UChicago, merit scholarships are part of the admissions process and can range from smaller awards to very significant ones for some students. These are awarded based on the strength of the application rather than financial need, and applicants are typically considered automatically for many of them when they apply for admission.

At MIT, the main way to lower cost is through need-based financial aid, not academic or talent-based scholarships from the school itself. Students can still pursue outside scholarships, but that is different from MIT offering institutional merit aid. So on the question you asked, UChicago offers more merit aid because MIT offers none institutionally.