Who is the best quarterback?  

You forgot Unitas and Tarkenton.

They play 16 games in a season now, they used to play as little as ten games a year. Most of the careers of the two I mentioned were played with 12 game seasons. The current list you mentioned have played 16 games in each of their seasons, so its hard to compare the stats since the number of games played weren't equal.
I do think Brett Favre was the best quarterback in the history of the game. I'm a lifelong Viking fan and don't care for the Packers, I always respected and admired Favre on the field and off.
The Mannings and Bradys and even the Montana teams had such a good supporting cast of players, their job was easier. I think Elway and Marino did more with what they had than the others, all things considered. I think that no one will ever play the way Favre did though. He is my pick for the greatest quarterback in NFL history.