I personally would choose MIT, but thats more a function of my research interests (and those of faculty at MIT Poggio, DiCarlo, Fiete in particular) than any other factors. What factors are you using to make your decision? Unfortunately I can't comment on the student life at either place, and I think thats probably what you were looking for in these responses. I'm not sure how many current grad students are checking this type of thread though.
Piggybacking off of your question, I am deciding between UCL Gatsby and NYU (and maybe CMU) for comp. neuro. If you (or anyone else) has heard or has any opinions about student life at any of these places, I'm all ears...