I would have to say Brett Favre...I don't know that he is the best ever, but he is definetly the toughest competitor to take an NFL snap as QB. His Ironman streak of game starts is absolutely incredible.
The bottom line is the no matter what else is going on in the game if Brett is still breathing you know your time has a shot.
Who's the Man?... J-Man, that's WHO!
Eat 'em Up, KATS!