I have a Carl and a Jumbo. As others have mentioned, both Carleton and Tufts offer excellent undergraduate education, but in different settings—a medium-sized university with easy access to a large city vs. a typical liberal arts college in a nice small town.
For an international student, both are convenient for international flights. It takes about 20 minutes to get to Tufts from Logan by Uber. It takes about 50 minutes to get to Carleton from MSP airport by bus. Both will give you great opportunities of immersion in American culture, unlike some colleges with a huge crowd of international students from Asia. If you miss authentic Asian food, you can easily get it at Davis Square and Harvard Square, but I don’t think there’s any authentic Asian restaurant in Northfield.
Both colleges are known for a non-competitive learning environment, but both offer challenging courses and you need to study hard. Most of the students, including my kids, would say that they study harder in college than in high school; however, in college you do have more free time and choices to pursue what you want to do. So, studying is much more enjoyable. Both of my kids spent most of their time on campus. The kid at Carleton probably went to the Twin Cities for fun only once or twice a year, completely happy and content with campus life. The kid at Tufts got more chances to hang out with high school friends attending colleges in Boston area on the weekends (and spent more money for social occasions).
Tufts only guarantees the first two years of campus housing. The off-campus housing typically costs more than the dorms. Carleton guarantees four years of campus housing. IMO, Carleton dorms are generally better than Tufts’. Carleton campus is really nice and cozy. Tufts campus is a little hilly, which helps my kid become stronger.
Both colleges have their share of cold winter; however, there seem to be more sunny days in Northfield than in Boston. In recent years, Boston seems to have more snow and rain. My kid at Tufts appreciated to get a raincoat and needed a sturdy umbrella. The kid at Carleton never used an umbrella there. The kid at Carleton never had a class day cancelled due to snow during his four years there. The kid at Tufts had several days off due to inclement weather.
Personally, I prefer trimester to semester calendar. It’s more fast-paced but you take less courses per term. Carleton’s winter break starts with Thanksgiving and students get the whole December off, a good time to be with family or get a holiday season job or doing research/internship/job-shadowing.
Both kids always got the classes they wanted to take. The kid at Tufts had a freshman English class of only 12 students, taught by an adjunct, along with some classes of 20-50 students. The kid at Carleton hardly had any class over 20. However, nowadays any lower level CS class in any college can be large due to popularity.
It’s important to have research experiences to apply to graduate school. It may be easier to get research opportunities and mentoring at Carleton, but you can certainly get it at Tufts, too. It all depends on your efforts. Professors at both colleges are very good at teaching, according to my kids (they often exchanged their classroom experiences with their high school friends in many other colleges). Both colleges are known for friendliness of the people there. Carleton is smaller in size, so it may give a closer feeling.
What is the most important factor to you? There’s no wrong decision. Both are very fine colleges.