I interviewed at both. Briefly (and incoherently) here's what I thought:
Brown has some big names, especially in Head and Neck and Gyn. If you are considering a Gyn fellowship then Brown has an advantage of having a famous attending with lots of consults and a huge women's hospital. In addition, Brown seems to have some decent collaborative research between pathology and other departments that I think residents could get involved in. In fact, when I interviewed there, they called in a pediatrician to come talk to me, spur of the moment, so we could chat about a project. Disadvantages about Brown: You end up traveling a lot between rotations - there are several hospitals that are part of the residency program, including one that is a bit of a drive away. And the residents are kind of a hodge-podge of people that didn't seem very comfortable with each other.
UMass doesn't have as many big names but has great facilities and good attendings. The disadvantage there is that you are physically isolated from the rest of the hospital community by being across the street. I also didn't get a feel for opportunities for resident research. I liked the PD there, he seemed very interested in his residents. However, I actually felt that the residents I met seemed a little unhappy. Could be wrong. Oh, and the clinical laboratory is amazing - they do EVERYTHING there because they are a regional referral center. Great opportunity to learn clinical chemistry if you like that sort of thing.
At the end of the day, the ROL is all about what you want to do (i.e. if you want research vs community practice, hemepath vs gyn path or whatever) and where you want to live. If you can figure that out at least partially, then all the rest will work out.
That's about all I have to say about that...good luck!