Favre is one of the most overrated players in NFL history as far as QBs go.
He has 1 SB and it was against a well overmatched Pats team with a QB that throw 4 picks and a return man that was really the MVP of the game. He piled up stats with a team that never ran in TDs and he would rather go deep on a careless throw then manage the game. Either he didn't know how to manage a game properly or winning was not his #1 concern.
Frankly I don't think he should be in the top 10 all time. I put him in the same group i put Manning, Marino and guys like that in. And he is not even the best in that group.