Many people have said this to me--and perhaps I'm just incredibly dense--but at least in terms of research I didn't see too much of a difference in environment between the two schools.
Yeeeeah... research is not what people mean when they say "environment"
But from your answer I can tell you're not the type to care that much and you should just pursue the best research match. Lucky for you, you're choosing between two word-class institutions so neither of them has objectively better research than the other. So this:
Mostly I want to know, where do you think the best research is happening?
is just a silly question. You'll have to pick which place seems to have the most interesting groups to you personally.
However, it sounds to me like you're more keen on Harvard. If you visited and liked the place, just go for it! You can't go wrong here.