Peyton Manning has more physical talent then Tom Brady.
Peyton Manning has been around football all of his life and I think the fact that his Dad was a Professional Quarterback definitely helped him pickup the nuances of the position faster.
However, I would take Tom Brady simply because he appears to "handle" pressure a lot more consistently then Peyton Manning.
Also, people forgot that for a while, he had no running game and had average to above average receivers to work with.
Honestly, I am surprised that more people are not voting in favor of Tom Brady as he seems to be the most similar Quarterback to Troy Aikman than anybody sense Troy retired.
Like Troy Aikman, many said he was a beneficiary of a great Coach, great Defense, a great System and didn't put up the numbers of other great Quarterbacks.
I think Tom Brady plays within himself alot more than Peyton Manning, where as Peyton Manning tends to put more pressure on himself.
JMO