It's always been a point of contention for me when people point to the Patriots defense when comparing Brady/Manning. The only argument (and it's a good one) to establish Manning's greatness comes down to his numbers and stat's. If you're going to compare teammates, it only makes sense to do so with the players surrounding the QB's (offense).
I've removed each QB's "injury year".
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Pro-Bowl offensive players on Peyton Manning teams, 15 years
Quarterback: Peyton Manning, 13 Pro-Bowl's
Left Tackle: Tarik Glenn, 3 Pro-Bowls (2004-2006); Ryan Clady, 1 Pro-Bowl (2012). 4 Pro-Bowls
Left Guard: Zane Beadles, 1 Pro-Bowl (2012). 1 Pro-Bowl
Center: Jeff Saturday, 5 Pro-Bowls (2005-2007, 2009-10). 5 Pro-Bowls
Right Guard: Louis Vasquez, 1 Pro-bowl (2013), 1 Pro-Bowl
Right Tackle: None
Tight End: Ken Dilger, 1 Pro-Bowl (2001); Dallas Clark, 1 Pro-bowl (2009); Julius Thomas. 1 Pro-Bowl. 3 Pro-Bowls
Wide Receiver: Marvin Harrison, 8 Pro-Bowls (1999-2006); Reggie Wayne, 5 Pro-Bowls (2006-2010); Demaryius Thomas, 2 Pro-Bowl's (2012-13). 15 Pro-Bowl's
Running Back: Marshall Faulk, 1 Pro-Bowl (1998); Edgerrin James, 4 Pro-Bowls (1999-00, 2004-05); Joseph Addai, 1 Pro-Bowl (2007). 6 Pro-Bowl's
Total: 35 Pro-Bowl's (minus Manning)
Pro-Bowl offensive players on Tom Brady teams, 12 years
Quarterback: Tom Brady, 9 Pro-Bowl's
Left Tackle: Matt Light, 3 Pro-Bowl's (2006-07, 2010). 3 Pro-Bowl's
Left Guard: Logan Mankins, 6 Pro-Bowl's (2007, 2009-13). 6 Pro-Bowl's
Center: Damien Woody, 1 Pro-Bowl (2002); Dan Koppen, 1 Pro-Bowl (2007). 2 Pro-Bowl's
Right Guard: Brian Waters, 1 Pro-Bowl (2011). 1 Pro-Bowl
Right Tackle: None
Tight End: Rob Gronkowski, 2 Pro-Bowl's (2011-12). 2 Pro-Bowl's
Wide Receiver: Troy Brown, 1 Pro-Bowl (2001); Randy Moss, 1 Pro-Bowl (2007); Wes Welker, 4 Pro-Bowl's (2009-2012). 6 Pro-Bowl's
Running Back: Corey Dillon, 1 Pro-Bowl (2004). 1 Pro-Bowl
Total: 21 Pro-Bowl's (minus Brady)
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Anyone that uses the talent excuse is full of absolute dog shit. If Manning's #1 best case for GOAT are his fantastic numbers, then it's pretty easy to see that he's always been surrounded by exceptional talent. Do great QB's make the talent around them better? Yes. But that can be said for both Brady and Manning, so I don't give Manning more credit for doing that with better talent surrounding him.
Anytime these two guys are on the field, their teams are generally favored, so a win-loss record doesn't tell the entire story. They both have great W-L records.
But how do Manning/Brady teams perform against the spread?
Between 2001-2012 (Only records I found, although i didn't search further because...well, I've spent enough time researching for this stupid post):
Tom Brady lead teams: 106-66-4 ATS (.614%)
Peyton Manning lead teams: 93-79-4 ATS (.540%)
Manning has more talent around him, has performed poorly in the playoffs, and is significantly worse against the spread (which tells me that he doesn't play as well as the general public gives him credit for). This is without touching on his indoor/outdoor splits, or his trouble in cold weather games (both of these things are real factors).
I think Manning is one of the greatest QB's of all time, which is a great accomplishment in it's own right. I just have a hard time placing him above either Brady or Montana.
Hell, for all the talk about Manning putting up "The all-time greatest regular season for a QB !!1!", it beat Brady's 2007 season by 5 TD passes and 671 yards. That was by throwing 81 more passes (Brady averaged 36 attempts a game in 2007, so more then 2 full games worth of passes) and against significantly worse defenses (I outlined this in another thread, but trust me, the defenses Manning played were significantly worse then the ones Brady played).
Again, Manning is one of the best, but I just have a hard time putting him above Brady regardless of my allegiances.