Belichick. He coached up Brady to what he is today. You have to give Brady credit for being coachable though. Bledsoe, Garrapolo, Cassel and others all looked good under Belichick, but I do concede that none of them would have been as successful as Brady. Brady is very good, but Belichick would have multiple rings without him, albeit nowhere near as many. 60% Belichick, 40% Brady. Brady wouldn't have been Brady on the Bills, the coaching just wasn't there.