It's hard to argue. The only competition is the Steel Curtain.
As a Pats fan, I'm biased, but... The Pats have to be the best team of the salary-cap era (post 1994). What Belichick and Pioli have done with a rotating cast of players is astounding.
True, but the success of the Patriots in the salary cap era says a lot about just how bad the NFL has become. By my reckoning, the 1999 St. Louis Rams were probably the last Super Bowl team in the NFL that would have been any better than 9-7 in the pre-cap days.
The Packers of the 60s won five NFL championships and the first two Super Bowls in a seven-year span.
What the Steelers did in the 70s and the Niners in the 80s was good, but does not compare to that record of domination over the greater part of a decade. As a Cowboys fan, it pains me to admit it, but I believe the 60s Packers were the greatest pro football dynasty of all time.
I think the only competition might come from the Browns of the late 40s and early 50s.