There is always the era thing to consider if you are going to compare straight statistics though.. today's game is more passing oriented than the game in the 50's and 60's. Statistics in football across the generations is more misleading than in say a game such as baseball.
That is what makes some of this so speculative in nature and is part of the fun in it all. If you want to base it of just pure stats.. one would have to consider the Lynn Dickey lead Packers O.. on numbers alone. But to pick Dickey over either is just plain silly.
My point is, that both brought different things to the table that both teams were geared for.. so one would have to consider what type of team you are building, what the role of the QB would be, and what era you want to consider in picking such a legendary team.
One could argue to the day is gone on both accounts, Favre or Starr.. and without the big picture neither answer would be truly wrong, IMO.
LOL.. as you can tell.. I am not a huge stats guy.. give me how they impact what you are trying to do on the field more so than the numbers they put in a book to be referenced.
"The oranges are dry; the apples are mealy; and the papayas... I don't know what's going on with the papayas!"