With a fantastic player like Tom Brady it's easy to make the case he is the greatest because his playoff and Superbowl success is now unrivaled. However, I think a case can still be made for Joe. Joe, like Brady, enjoyed most of his success with one team, the 49ers. But unlike Brady, Joe was also able to prove his greatness by playing and succeeding with a different team. In his first year with the KC Chiefs in 1993, Joe led his team to the AFC Championship game and their most successful season in 22 years. In 1994 he again led the Chiefs to the playoffs. Along the way he beat his old 49ers team; a much more talented team led by Steve Young that would go on to win the Superbowl that year. He also elevated the Chiefs to beat their main nemesis: John Elway and Mile High Stadium, ending two curses in the process. The Chiefs hadn't beaten the Broncos at Mile High Stadium in 6 years and Chiefs coach Marty Schottenheimer had his own record of futility against Elway dating back to his days as coach of the Browns, but instead of Elway once again breaking the Chiefs' and Schottenheimer's heart, it was Montana who executed the last-minute game winning drive to exorcise those Elway demons for a Chiefs win. Montana didn't win a Superbowl in his two, and ultimately final years with the Chiefs, but Schottenheimer has since said the '93 Chiefs team was the greatest team he ever coached in large part because he had Montana.
In contrast, Brady has never had to play for anyone else but Bill Belichick. I think he would be great in other offensive systems but he's never had to prove it. On the other hand, the Patriots and Belichick have had to prove they could play without Brady and they've succeeded. In 2008 they went 11-5 with Matt Cassel, a backup QB in college, at the helm, and this year they went 3-1 with the likes of Jimmy Garopollo and Jacoby Brissett. So the question is, if the Patriots can succeed with marginal talent like Cassel, or unproven talent like Garopollo and Brissett, is Brady the true secret to New England's success or is it really Belichick?
Now, before you say it, yes, the 49ers also proved they could succeed without Montana but they did it with Steve Young, one of the greatest college QB's of all time who then became one of the greatest NFL QB's ever. Young isn't proof that any QB could have succeeded in SF's system. He was an elite talent to begin with. On a personal note, I always use Steve Young as a counter argument for anyone who tries to promote the idea that John Elway was the greatest QB of all time. I always respond by saying Young could do everything Elway could do but he did it better. Just look up his passer rating and rushing stats and compare the two QB's. And since no one thinks Young is the greatest QB ever because he wasn't better than Montana, no one should think Elway is the greatest either.
But I digress. The point is, Montana was able to prove his greatness outside of SF. Brady has never had to prove he can be great without Belichick. Of course, the same could be said about Belichick - he's never been able to prove he can win a Superbowl without Brady.
So that leaves us where we started. I have no qualms with anyone making the argument Brady is the GOAT. He has an extremely solid case, but for those of us who still think it's Montana I think we also have solid ground to stand on.