@WiseStudent makes an important point: the campus cultures at Grinnell and Davidson are very different. My daughter is a very happy first year at Grinnell. When we visited Davidson, I couldn’t even get her to go on the campus tour after the info session, because it revealed that about 30% of students are sorority or fraternity members.
I can’t imagine that there’s enough difference in math research opportunities to make a person who would be happy at Grinnell willing to settle for Davidson and vice-versa. Have you visited both schools? My daughter didn’t visit Grinnell until after she was accepted because we live in the Southeast.
Good luck with you decision.