The top two rushing defenses in the league go head to head, so this will obviously turn into a passing contest.
Peyton is obviously better than Romo (I am a Romo fan, but let's be real.)
Dez Bryant is the best receiver on the field, but the next three best receivers belong to Denver.
Witten is better than Thomas, but Thomas is up and coming.
Denver has a much better O-line than Dallas, but Dallas has a much better pass rush.
I think Denver also has a more consistent secondary. Dallas can make more plays back there, but Denver's secondary is a bit better. (They give up a lot of yards in garbage time)
I see Manning taking advantage of the holes in the Dallas Defense. He will get sacked a few times, but he will eventually put up about 32 points and Dallas will only get to about 24.
Denver -3 -120 at bookmaker is a solid play IMO