Hah, so Bill Simmons weighed in on this very topic in his mailbag today:
And you can’t have the “Best QB” conversation without these five guys being involved: Brady, Manning, Montana, Elway and Unitas. (Every other candidate comes with a “But … ,” whether it’s Marino, Favre, Young, Bradshaw, Luckman, Graham, Baugh or whomever.) Year after year, those five guys gave you the best chance to contend — of anyone — as long as you surrounded them with a half-decent team. I don’t think someone like Aaron Rodgers cares about being remembered as the GOAT; he just wants to win some titles, make some money, stay healthy and turn that list from five to six.
http://grantland.com/features/that-championship-mailbag-2/