Three amazing choices! Congratulations!
These three schools are more similar than different, in that each is a top small liberal arts college with the associated features: tight campus community, small classes, great research opportunities with professsors, interactions with professors out of class, etc. In addition, each has a very beautiful campus, and none has fraternities or sororities.
Here are some strengths of each:
Bowdoin: best college town of the three, polar bear mascot, its coastal Maine setting is great if you like proximity to both ocean and mountains, most selective of the three
Middlebury: campus of breathtaking beauty surrounded by mountains, best buildings/facilities of the three, world famous for language study
Vassar: great theatre opportunities for both viewing and participation and famous alumni in this field, the only of the three to be originally female resulting in a legacy of gender equity, a decidedly liberal bent, the least isolated of the three colleges in that is has the shortest journey to a world-class city (NYC) but still far enough away that most would only rarely visit the city on a weekend, gorgeous library and campus
I know two former psychology majors from Vassar. One is a clinical psychologist and the other is a college professor of psychology. Both loved the department at Vassar.
Really, you can’t go wrong here. Pick by “feel.” Which do you just plain like the most? If unsure, visit each if you can. If you cannot visit, read a bunch of college guides and online sites and maybe ask admissions if you can speak with a current student.
Congratulations on having incredible options.