Moving to hSDN.
While I dont have a strong sense of either school, Tufts and Vassar are very different schools. In my personal opinion, small liberal arts colleges like Vassar typically provide more nurturing environments for their students in general, not just pre-meds.
Receiving a quality general education that will also allow him to achieve his goals, whatever they might be (and they are very likely to change) should be his priority, not being a premed.
Also, I encourage your son to make an account and ask questions on the forum himself.