Will you be able to visit? That might clinch it.
-How the location affects the overall experience (close vs far from big cities)
Amherst has a lot more stuff in walking distance of campus than Tufts does, was my impression at the time we visited Tufts. We drove from there to a cool commercial area with thrift shops and restaurants about ten minutes away. Boston is close (30 minutes or so) though the Tufts tour guide we had said hardly anyone goes there regularly.
The Amherst area has 5 colleges, 2 right in town and one of the two has 25,000 students so that makes it a very college-ey college town. Boston is 2 hours, NYC is 3 and there are buses that go to both every day, nonstop on weekends. Speaking of buses there’s free bus service throughout the area linking the 5 colleges with each other, with shopping, etc.
Amherst kids do summer internships in big cities. They don’t really do them during the school year but that may be an option for Tufts re: Boston.
-Socioeconomic Diversity
Amherst wins this one. Tufts has more kids from the top 1% than the bottom 60% according to the NYT article: https://www.nytimes.com/interactive/2017/01/18/upshot/some-colleges-have-more-students-from-the-top-1-percent-than-the-bottom-60.html?_r=0
-Classes
What’s your concern here? Difficulty, size, variety? Most classes at Amherst are small, all are taught by professors and you have the option of taking classes at any of the 5 area colleges if you don’t find what you want at Amherst. that said, most Amherst kids stay at Amherst for class, more often kids from the other schools go there for classes.