I think a lot of Brady's talent is masked by Bellicheck. I don't know if he would be as great on another team.
I am not a Pats fan, but I don't hate them either like I do the Seahawks, but both Brady and Belichick are great at what they do. At least with Belichick you don't have to be young so he will remain a constant as far as his ability. Brady, perhaps the greatest or up there with Montana, Marino, and Manning (all Ms, hmm), can only play for only so long before he's not useable in the NFL. Whether this year or a few years from now is his last, he doesn't have anything left to prove.
Belichick, on the other hand, could keep on working and close in on the all time coaching records like career wins, SB wins, division wins, etc.