Hi, I'm at CMU and I work a lot with the ML department. One thing you're going to get at CMU and not at Harvard is access to a strong body of other excellent ML, LTI, CS, Neuro, RI, etc researchers. Everyone here collaborates all the time and you would have access to not just one or two great ML reseachers. Also, Pittsburgh is a pretty good living city. It's cheap and it has great resources. Besides, you're going to be working your ass of for 5 to 6 years, you wouldn't see much of Boston anyway