Peyton Manning's playoff record is really unimpressive, at the end of the day it comes down to championships, I'm not saying just because you win a championship you are better than somebody. For example, Dilfer is not better than Marino.
However, when comparing players that are as close as Brady and Peyton, I would take Brady based on playoff success difference. . The only QB who in the last 10 years who can compare with Brady's playoff success is Roethlisberger and he has been carried greatly by an unbelievable defense, if Peyton was on Roethlisbergers teams, he'd have won at least 3 super bowls.