IMO, you simply can't compare today's QBs to QBs of yesteryear because the rules are just so damn different.
Except we can!
There are stats that normalize numbers based on the offensive environment of the era.
And even when adjusted for the increased offense, Manning absolutely smokes a guy like Elway so convincingly that the only way to formulate a pro argument for Elway against Manning is anecdotal fuzzy memory bullshit.
I'm going to attempt to explain this, but i'm probably wasting my time, since it's hard enough to get baseball fans to understand shit like this, and baseball fans compared to NFL fans in terms of sophistication is like comparing modern man to neanderthals.
100 is average. 110 would be 10% better than your peers. 90 would be 10% worse than your peers. The same as OPS+ or ERA+ in baseball.
We'll stick with the basics, but even the others don't look good for Elway, so let's quit while we're ahead:
ELWAY
Yards per Att: 104
Comp%: 101
TD%:102
INT%: 107
QB rating: 105
Manning
Yards per Attempt: 115
Comp %: 120
TD%: 120
INT%: 108
QB rating: 120
Again, these numbers are normalized so you can compare across eras. The work is done for you.
Manning smokes Elway in the regular season to the point it's a squash match, and he has better overall playoff numbers no matter what myths people tell you.
So if your argument is Elway > Manning, you are basing it on 2-5 in the Super Bowl vs 1-1 the Super Bowl. Let's be more sophisticated that that.