On an era adjusted basis, Rodger's 2011 season was 3rd best all time, wherein he played 44% better (see the ANY/A+ column) than his peer group. Manning was 53% better than peers in 2004, and Marino was 50% better than peers in 1984. Peers is defined by the three year average of all QB's for that stat, the year before, the year of, and the year after. If it is the current year, then the year after is left off as it doesn't exist yet and only two years are used (so the 44% better than average could change once next year transpires).
So that's Manning, Marino, Rodgers, Brady, Young in descending order.
If one wants to use pro-football-reference's proprietary AV (approximate value) calculation (the far right column), Rodger's 2011 season was the 2nd most potent behind Tom Brady's 2007 season and Steve Young rounds out with 3rd, 4th, and 5th most potent seasons.
This is the site I use, I am sure there are others, but I can only assume the Brady 2007 season, the Rodgers 2011 season, the Manning 2004 season, the Young 1994 season, and the Marino 1984 season will be at least in the top 10 using other formulations.