Montana played in a passer-friendly system and era yet he was the first QB to retire with a higher career passer rating than Otto Graham. When we are talking about who the best/greatest QB of all time there is no doubt that it was Otto Graham.
Graham played from 1946-1955, 10 years. All 10 years he was named All-Pro, all 10 years he took his team to the championship game, winning 7 of them. He ranked lower than 3rd in only one season in passer rating and was 1st 4 times. He is 2nd only to Steve Young in rushing TDs by a QB 50 - 55 (and no, he wasn't a single-wing TB).
Otto Graham was the Wilt Chamberlain of pro football, his stats blew away everyone else and some have STILL not been surpassed. His career average of 9.0 yards per pass attempt will likely NEVER be broken. His career winning percentage is over 85%, Staubach is 2nd among QBs with over 10 years at 75.6% (Brady is at 77.5% but he has only played 8 seasons).
When you look at his stats you have to take into account the era when he played and compare him with his contemporaries, (Waterfield, Van Brocklin, Tittle, Layne, Baugh, Luckman, & Blanda: All HoFers) they don't come close! The rules did not favor passing, even the ball was less aerodynamic.
You can check out his stats at:
http://www.pro-football-reference.com/players/G/GrahOt00.htm
Without a doubt the greatest QB to ever play the game.
The only knock people have against him is that he played 4 years in the AAFC, a rival league from 1946-1949 but the Browns won the title their first year in the NFL so they couldn't have been that weak. Also, no one docks Len Dawson, Joe Namath, or other AFL QBs who played in a weaker league but the old guard NFL owners really hated the AAFC and especially the Browns and only recently accepted stats from that league as "official".
Even so, the Browns played in the championship game all 6 seasons in the NFL and won it 3 times (1950, 1954, 1955). Graham went out a winner, TWICE. He retired after winning the 1954 championship game but Paul Brown begged him to come back for one more season in 1955 and they won it all again. Graham led the league in passing that year with a 94.0 passer rating. Staubach is the only other QB who went out as the top rated QB.
I could go on and on (too late)...
P.S. I HATE the Browns but I rank Otto Graham as the top QB of all time and Paul Brown as the greatest HC ever. Truth is truth.