^Actually, for an international student, having 4 campuses which are extremely residential and wealthy (hence providing hosts of free entertainment) would be extremely important.
In addition remember that undergraduates will only take 1/3 of their classes in their major - OP is unlikely to exhaust the academic offerings at ANY of the universities, but the ability to take seminar-style classes with the nation’s best students would be a great bonus to the motivated UMass student.
It’d be important to know whether OP got into SB’s Honors College as this would mitigate some downsides (in particular, for someone who wants to get into research, being in the honors college at a research university makes it much easier to join research project that they’re competing for with graduate students, vs . “regular” undergraduates). Ultimately, my evaluation of Stony Brook isn’t strictly for its science offerings - I think everyone will agree they’re superb- but rather the fact it’s very lonely for international students because it’s a heavily commuter/suitcase campus that isn’t geared toward building a new community for those who come from too far away to have any ties to the area.