DENVER — Only one of them can be the greatest. Peyton Manning could be the one — owner of a record four, working on five, Most Valuable Player awards, current holder of NFL single-season records for passing yardage and touchdowns and architect of a career-reviving second act, the likes of which has rarely been seen in any sport. Tom Brady could also be that man — leader of five Super Bowl teams and winner of three titles, one-time holder of some of the records Manning holds now and author of an undefeated regular season.