I am a resident at MGH, and very happy here, as is the overwhelming majority of my colleagues. I think as a whole, we are a happy, down to earth and supportive bunch who all work very hard. I am constantly impressed at how much my colleagues love what they do and how committed they are, and have found that this is so important when you are doing a job as stressful as this for as many hours a day that is required. This place can come across as a bit intimidating on interview day (which I suppose is kind of the point) so I can understand some people coming away from that with negative feelings.
I do know residents at BWH as well as former BWH residents who are now fellows at MGH, and after several long discussions contrasting the two places, I found that the overall opinion from within the two places is that MGH residents probably spend more hours in the hospital, if you will, than the Brigham. I think that despite the impression that people have that we are a more unhappy bunch than the Brigham residents, we tend to be a more cohesive bunch, and spend more time with each other socially outside the hospital.
As far as the OP's original question regarding research, I don't think either one is necessarily more or less research oriented, except that most residents at both programs (but not all) end up doing some sort of research. Both the hospitals themselves as well as Harvard has a lot of funding, which helps alleviate the stress on the resident of finding grant money. I think, though I have no figures to prove so, that more residents go straight through at MGH than at BWH. MGH residents do the majority of their rotations on-site, with rotations at two community hospitals and at Boston Children's (with the BWH residents). We have a Level I Burn center, and a Children's Hospital (including Pedi Trauma) on-site which BWH does not have (though they still see some burn patients as I understand). BWH experience includes rotations at the VA, which we do not have. I think the residents at MGH probably do more in the ORs sooner than BWH, but the numbers all equal in the end and the clinical experience overall seems very similar.
If anyone has any specific questions, please feel free to PM me.