Arm strength very similar. Release, Dan gets the nod. Accuracy has to go to Dan. I've yet to see anyone throw into triple coverage and regularly put the ball where only his receivers could catch the ball. Field and defense recognition has to go to Manning. Overall teams similar except Peyton has always had a 1000+ yard rusher though other than 1 year the Edge wasn't a game breaker. But Dan's D was probably more consistent over his career.
As far as receivers go. Harrison can be mentioned in the same breath as Rice, Holt and Ward. Neither Duper nor Clayton were even close to as good as Harrison. In fact, Reggie is probably as good if not better than both Duper and Clayton were. Those two were made far, far better by Marino than they actually were. Don't forget, there was only one season that they both had over 1000 yards and only 2 total that either one had 1000 or more yards receiving. I love the guys but they definitely can't be considered top 20 of all time and Harrison certainly can, Reggie has yet to be seen.
If Marino had either Harrison or Rice, he'd have thrown for 60+ tds in a season and over 6000 yards. In fact, if Favre or Elway had a Harrison or Rice they too would have shattered anything Peyton has done so far. No one had better pocket presence than Marino. I've never seen a qb move slower or less and avoid more sacks than Marino did. The guy could feel pressure better than anyone ever has in football.
My money is still on Dan. You take anyone that's approached his numbers besides Elway and Favre and put the receivers that those few qbs have had on Dan's team and you're looking at numbers half again higher than the numbers Dan compiled.
Top QB rankings in my book. Elway, Marino, Unitas and Favre in that order. Could Manning go top 3 and userp Unitas or Favre, definitely. Will he ever replace Marino or Elway, not in my book no matter what records he breaks.