Based on skill. Kinda like my personal Madden rating: arm strength, accuracy, etc. Championships are important but not the end all imo especially in a team sport. I hypothetically put each player on a team where all their team mates and opponents were equally matched robots, and I think Marino and Manning are the most skilled qbs. The perfect example is Wilt and Russell. Yea Russell has 11 and even beat Wilt head up a few times, but there is no doubt in my mind Wilt is a better baller.