hey, I am waiting to hear from both of those programs and would like to know more as well. Since Baystate is a major affiliate of my school (TUSM), I know that it has the advantage of having a major Level 1 trauma center with good ER exposure, if that is something you'd value. Also supposed to be a very nice hospital, and about 20-35 3rd year students from Tufts choose to spend their 3rd year at Baystate. I will be going out for a few 4th year rotations myself. They also have a women's health track. from what I hear, the program tends to attract a number of residents with families, and the schools in Springfield are not too bad if you have kids.
I think UMass has more of a national reputation for IM, and is known for outstanding primary care training. Their program also seems to attract a lot of UMass Med grads as residents, which I think attests to the UMass students' respect and admiration for the program and faculty. Although Worcester is not a particularly attractive city, it is about 45 minutes from Boston via car or cheap commuter rail, which IMO is a big advantage.
My understanding is that both are solid programs, but their reputation suffers b/c Worcester and Springfield are considered much less desirable locations than Boston. I'd be more inclined toward UMass at this point for the reasons mentioned previously, but we will soon see. And I don't intend to turn down an interview offer from either! good luck.