I wouldn't call him the greatest ever. But he's better than Peyton by a long shot.
Here's my ranking:
1. John Elway (unlike Brady, he took three teams with subpar defenses to the Super Bowl. He played five in all, six AFC Championship Games. I believe had he been on the Niners, he would have won at least five Super Bowls.)
2. Joe Montana (was Mr. Clutch. But he had more talent around him than Elway, including Jerry Rice for two of his Super Bowls.)
3. Tom Brady* (nine AFC championship appearances, six Super Bowl apperances, four wins, three Super Bowl MVP. Yes, he's had good defenses for the first three Super Bowls, but his defenses were average the other three and Brady was still competitive. Never beats himself. And has played with average running backs and average receivers for most of his career.)
If he wins another Super Bowl, I may have to move him above Montana, maybe Elway.