Thanks for all the advice! After reading this, I'm now heavily leaning towards Brandeis/Columbia.
For the record, I only applied to small schools b/c I felt that larger schools were not my cup of tea. I wanted to do engineering at Tufts but got rejected, so now I'm left with liberal arts engineering. Moreover, Brandeis' version of the 3-2 program requires me to do research at some point, and the school's proximity to Boston opens up a lot of internship opportunities, so getting good research done there shouldn't be too difficult. There's also 260 clubs at Brandeis, so I should be able to find one connected to engineering. And, of course, Columbia is a great engineering school (and an outstanding school in general), and I'm fairly sure that engineering is what I want to do with my life.