Rather than decade per se, I'll go with a ten year period split between two decades. Nothing could, arguably, beat the mid-50 thru mid-60 period. Having had the great fortune to see so many of Jim Brown's games on the tube (in Buffalo since Cleveland was the closest NFL franchise) and many of Johnny Unitas' during that period, nothing can compare. In my mind, they were to two finest players in NFL history, which makes that 10 year stretch unbeatable.