So obviously it's very subjective and there will always be an argument/discussion short of Brady or Manning reaching 5 rings with continued ridiculous stats, and even then there might still be an argument. Personally I do think it being the salary cap era factors in a good bit too for the title of GOAT.
My personal list for top 5 all time goes:
#1 Joe Montana, pretty self explanatory, ring argument, and pretty good stats.
#2 Tom Brady, I personally already hold him at #1 and I'd move him to first objectively if he can just makes one more sb, and it's unquestionable imo if he wins one more sb)
#3 Dan Marino, Idgaf about the ring argument, yes Superbowl wins should factor in some but they arn't the end all be all, as far as i'm concerned too many people forget it's a team sport sometimes and get caught up with all the media hype. Marino might have been the best QB ever, rings and all on a better team, and I don't mind the argument for placing him at #1
#4 Peyton Manning, one more SB with his stats and awards might have tied or surpassed brady's #2 rank in the eyes of many.
#5 Brett Farve, People really do underestimate just how hard it is to play at the level he did for all those years injury free, he was basically the iron man of the NFL! And he did it in an era where rules didn't favor offense as heavily as they do now
Notable snubs/omissions: John Elway, Steve Young, and of course none other than Tim Tebow!!!
Lastly I should say though it's way too early to even begin to put him in the discussion, I hope Matt Ryan is #1 when it's all said and done, his stats definitely compare favorably to Mannings first 6 seasons, now he just needs the rings and continued consistency. Though my biggest fear is he ends up the next Marino! Curse you Atlanta sports, always tantalizing us with a team seemingly good enough to win it all (looking at you braves, falcons, dawgs) and then always falling just short!!!!!!!!!!!