Year's best, worst RBs, receivers

It's not surprise Adrian Peterson was the NFL's best RB in 2012. AP Photo/Genevieve Ross

The 2012 season in a nutshell: Calvin Johnson broke Jerry Rice's record. Adrian Peterson threatened Eric Dickerson's. The league was overtaken by a rookie class the likes of which we may never see again. And the best four quarterbacks in football are now the same guys who have been the best four quarterbacks over the last half-decade or so, especially when viewed through Football Outsiders' exclusive statistical lens.