Of the New York programs, I would pick NYU over Cornell. NYU residents rotate through Sloan and the overall clinical training seemed better. The morning report at Cornell was a real let down -- only 2 of the 20 residents did any talking and the whole thing was run by the attendings. At NYU, it seemed like interns and residents worked harder but, in the end, wound up being more confident physicians. Plus the chairman of cornell is stepping down (the chair of penn is taking over). This may not have any affect on your future academic career, but any kind of change can potentially have destabilizing effects. So for all of these reasons I would be wary of Cornell. I didn't interview at BI so I can't comment on that, but I have heard good things. Also I think Boston is an easier city to live in than New York, but that's a personal preference.
Cornell residents spend a considerable amount of time at MSK. I know several interns who are already starting research projects there. Residents here consistently match quite well in Heme-Onc.
Being a cornell PGY1 and having worked there with NYU interns and residents, I saw no superiority in their level of clinical ability when compared to Cornell counterparts. I've said this before on SDN. And as far as how hard interns work, I think we work as hard as any program in NYC. This is a very frontloaded program.
With regards to Dr. Nachman's stepping down, he is an amazing physician and it is always a loss when someone like that retires. That being said, he and Dr. Pecker spent a massive amount of time choosing the new chair, and I trust their judgement in that regard. The negotiation of the new chair's contract is going to bring some changes to the program, all of which are considered positive per Dr. Pecker.
Finally, mdcharak, i support your decision to NOT come to NYP/Cornell. To everyone puttin together your rank lists, go where you felt is the best fit for you based on gut feeling, future goals, training, lifestyle, city, etc... whatever you feel is most important. mdcharak did not feel cornell, and I wish him the best of luck where ever he does end up training. Take care when reading posts on the interweb about programs based on a 1 day interview....