Those are three wonderful choices. Williams is the small liberal arts college version of an Ivy league school – it is considered in the top 3 of small liberal arts colleges, along with Amherst and perhaps Swarthmore. In my mind, arguing about which of those small schools is “better” is the equivalent of arguing whether Harvard, Princeton or Yale is better – they are all superb, but one may be a better fit for a specific student. At Williams, the education and opportunities can be transformative for a student who is coming from a first gen background, and they would not have admitted a student they did not know would succeed. The focus on community at Williams as described above, can really help a first gen student be welcomed, and feel integrated. Williams is a distinct physical experience – a beautiful location in the Berkshires of Massachusetts, remote from the bustle of city life.
Colby has been making a strong push to develop a more diverse student body, I heard last year they had something like 20 Posse scholars. One question with Colby, since it is making a push on diversity, is to find out whether the school is also offering support, programs and funding to help first gen or low income students whose families may not have the experience in navigating the way through higher education in the States – advising, course selection, access to professors, resources for summer internships, study abroad etc. (Those are questions to ask at about all the schools, really, but it seems like Colby is relatively a newcomer to increased diversity on campus, you would want to see if the programs have caught up with the increased diversity in enrolled students).
Mac is known for its global focus and has a higher percentage of international students. It is also the only school located in an urban area (though hardly like an NYU) – more of an urban residential area, with access to all the arts, culture and diversity of the Twin Cities available.
Since you are able to visit Williams and Colby, see how each feels. As between those two, Williams probably has a longer track record of working with 1st gen and students from diverse experience, and with the distinct structure of the community, might provide a smoother transition to college. But it is possible Colby could just “feel” right, in which case, trust your instinct. Mac is a wonderful school, but academically not at the level of Williams (and people could argue whether it is at the level of Colby). Perhaps if neither Williams nor Colby “feels” right, then turn to Mac as an option. But if it were me, I’d suggest Williams is the overall top choice, with perhaps Colby and then Mac.
Congratulations, and good luck!