In recent years, many NFL fans have argued about who is the best quarterback, Peyton Manning or Tom Brady. In 2007, Brady was better, but Manning holds the better overall quarterback rating. Still, one could argue that Manning has played more years than Brady has.
Brady was unexpected to become the great quarterback that he is today after being drafted by New England in the sixth round. Manning, however, was expected to be great and was drafted with the first overall pick.
Manning has won a lot, but Brady is a Super Bowl ring collector. He has three already, and nearly won a fourth. Manning has one.
It's probably too early to be able to tell which one is better. Most likely we will have to wait until the end of their careers. But you can be sure of one thing—whenever these two meet in the future it will be a hard fight.