MIT definitely has the most penetration of the 'hacker' culture. If it came down to MIT vs Harvard, I would personally choose MIT. Out of all three, MIT tends to be less elitist, from my personal experience.
"Less elitist" may not appeal to someone who announces on HN that he or she got into these three colleges. Harvard it is!
I can't really vouch for Stanford either way though, as I've never been there or really worked with Stanford grads/students close enough to have an opinion.