Cingular is about to revise their BB plan costs (there is a whole thread on this and I would advice looking at it and there is no need to bring into here). I would say look at both in depth and ask people who use their service in the MA area and what their thoughts are. I don't think I can (located in NY) or any one (located in diferent states) can tell you which one to go to unless if the person is with such provider in the same area as you are. One would realy need to do the home work to be sure that the right decision is made. Cingular gives a 30 trial period and T Mobile gives a 15 day one so take advatage of that to test and see what suites best.
BB 8800c / 8100c / 8700c / iphone3G