Sheraton Malpensa (Marriott) hands down. We always stay there when flying MXP-JFK. It's at Terminal 1 above the train platform and a 1 minute covered walk from the hotel to the terminal. It is definitely much more relaxing to spend the night at the airport and have a calm morning. The alternative of staying in Milan and getting up VERY early to get to Malpensa for an AM flight is not at all attractive. There is another Marriott brand alternative @ MXP - the Moxy - and it is cheaper but requires taking a bus to get to the terminal. The Sheraton is by far the best choice.

During the walk make sure to stop and see the words inscribed on the walkway.

“tutti i passi che ho fatto nella mia vita mi hanno portato qui, ora”
“every step I have taken in my life has led me here, now,”