In terms of smaller schools, Hamilton has strong political science (or at least, my recent college graduate keeps bumping into Hamilton grads who are working in politics), is cold, has greek life which does not dominate campus. Amherst is one of the top 3 small liberal arts colleges and is highly regarded for its PPE program, and has an open curriculum (few mandatory classes) which gives the student a lot of flexibility to study different subjects. It is in a lovely part of Massachusetts, a little easier to get in and out of than Hamilton. Heading to the midwest, Denison has the Lugar program in Political Science, which focuses on US politics or international, and includes an internships component, is diverse, about 30 minutes from Columbus which makes it more accessible for travel. Macalester in Twin Cities, Minnesota (talk about cold!), is well known for its international focus, and has a diverse student body.
The mid-size university 5-15,000 undergrads, can be tough to find a good match. Some of the undergrad populations at the Ivy league schools are in that size – Columbia, Princeton for instance – but there is a large graduate student population which brings the overall size of the institution way up. Notre Dame, Northwestern, Duke, Vanderbilt, Washington University in St Louis are all mid-size universities, highly competitive for admissions as well. Only ND and Northwestern have serious winter snows and frigid temperatures, though depending on what you are used to, the milder winters in North Carolina, Missouri etc. could feel cold enough!
You might keep an open mind about professor interactions in the truly large schools – my kid went to the University of Wisconsin and, as a double major in humanities and social science, had very close relationships with his professors. There are structural ways to create opportunities for getting to know your faculty better, from taking Intro level Honors classes where the faculty leads the discussion section as well as gives the lectures etc. Apart from a few intro classes in his major, most of my kid’s classes in his major at UW were 20-40 students, and once he was in his 3rd year and beyond, many were fewer than 20 as they were research seminars. A long way of saying – I don’t think there is a substantial difference in student-faculty interaction between the mid-sized schools and the large schools, for a student who is motivated to reach out to develop relationships with faculty.