Fit + visit impressions--as the decision date neared, I realized that I liked the emphasis for my particular program at TC a little more than the emphasis of the program at Vandy. It was a little more specific toward a certain career goal. Additionally, when I went to visit both, my advisor at TC was incredibly helpful and enthusiastic about her students' research, whereas Vandy could not even scrounge up a professor from my program for me to meet with, and I found out that my primary POI was leaving. It was't an impressive weekend.
Also, my SO was thinking of applying to Columbia, so it would have made things much easier on that end too.
Turns out, I think these initial impressions weren't very indicative of the experiences I had at TC or would have had at Vandy. I think I would have been quite happy at Vanderbilt, plus a little less in debt. But I guess I don't have any regrets; they're both fantastic schools.