These are 2 pretty different schools and both great options. Academically, I don’t think one is going to stand out as better than the other. You might find Tufts to be less of a culture shock than Carleton as a result of its size and location. There are a lot of Asian students there and in Boston in general if that matters.
Then again, if you are looking for a college experience that is quintessentially American, Carleton might appeal. It has a reputation for being very friendly (which is a generalization that extends to the Midwest.)
Man, I echo other poster. Really different options, but both great. I also agree about the culture shock.
One thing I know Carleton does well in terms of intl students is that they come to campus a week early, maybe more, and the college works to acclimate them to American life … setting up bank accounts and such. Ds’s roommate his first year was a Chinese international, and the school seemed to do a great job easing them into college life. Is there something similar at Tufts?