Where do the 2011 Packers fit in? How about the 2007 New England Patriots? The 1985 Chicago Bears? The 1984 San Francisco 49ers?
And of course, the 1972 Miami Dolphins... the last (and only) team to go unbeaten and WIN the Super Bowl title.
The overwhelming choice is the Chicago Bears of 1985, which went 15-1 and steam rolled the opposition in the post-season while winning the Super Bowl.
The Bears outscored the opposition 91-10 in the three post-season victories.
That post-season stretch is the best ever in terms of sheer domination. However, when talking about the best defense ever for a single REGULAR season, look no further than the 1976 Pittsburgh Steelers.
The Steelers were back-to-back defending Super Bowl champions and then started out 1-4 in the first five games of the '76 season, also losing starting quarterback Terry Bradshaw to injury along the way.
What followed next was simply incredible.
The Steelers pitched five shutouts and allowed an amazing total of just 28 points (3.1 points per game) in those final nine games. It was the greatest stretch of defensive dominance in the history of the NFL.
Included in the dominant run was the fact that Pittsburgh's defense did not allow a touchdown for 22 quarters in one stretch. They also did not allow a touchdown in eight of those last nine regular season games.
There are many who will argue for the 1985 Bears or even the 2000 Baltimore Ravens defenses as the best ever in a regular season, but what the "Steel Curtain" did during that nine game stretch that led to a 10-4 finish after the poor 1-4 start was indescribable.
Need more proof... well here is some VIDEO evidence of the greatest regular season defense in NFL history... the 1976 PITTSBURGH STEELERS.