So many variables.
Otto Graham - Played on the most dominant team of the era hard to say what he was capable of if he were with a lesser team.
Slinging Sammy Baugh - My god there still has never been another pure passer like him.
Johnny U. - The man was a winner, called his own plays, good teams, bad teams, whatever, he won. Played in the non wuss era, no face cages just a single bar, no halo rules, no rib pads, no roughing the QB calls, In today's game the man might be a god.
Joe Montana - Another winner, not always surrounded with the "best" talent (except the offensive line). The man made the system work, the system made the man a star. Had that intangible ability to carry a team on his back when things were not going well, and the ability to get every ounce out of the team. Leadership far more important than raw talent.
All the others ... well that is why they are the others.