It is no accident that the teams with the most championships and Super Bowl appearances are high on the lists...
1960's Green Bay won a lot of championships, played sound across the board, but not a dominant defense alone. The AFL coming around and forcing the merger with the NFL changed things with the passing game and more wide open offense and TV friendly play. The sport was growing ever since the '54 NFL title game (Baltimore and New York Giants), but the defense was not the selling point.
1970's Miami, Oakland, and Minnesota (Purple People Eaters) were great, but Pittsburgh's Steel Curtain and Dallas' Doomsday Defense were the top of the league for the era...
1980's Chicago Bears (1984-1988) were some of the most intimidating and dominating defenses of any era. The legendary 1985 team is frequently seen as the best because they won the Super Bowl and absolutely mauled teams along the way - back-to-back playoff shutouts (20-0 vs. Giants, 24-0 vs. Rams) and at the time put up the biggest blow out in Super Bowl history with the 46-10 crucifixion of New England. What many people don't realize is that the 1986 Bears went 14-2 and were statistically BETTER in yards allowed and points surrendered, they were BETTER in '86 than '85 by many metrics - but because of a hideously flagrant late hit by Green Bay's Charles Johnson on QB Jim McMahon that ended his season with a separated shoulder in November (a play where Johnson picked up McMahon AFTER a pass was thrown and body-slammed him on his throwing shoulder, one of if not the cheapest, most cowardly plays in NFL history). They were the most intimidating and vicious defense of the era.
The Lawrence Taylor-led, Belichick/Parcells coached Giants also had great defenses throughout the era. Washington and Joe Gibbs and San Francisco and Bill Walsh were more known for their offenses, but they did manage to have strong defenses too.
1990's and beyond was when the league really began changes rules to favor the offense and changed the way defense was played. Pittsburgh in the 70's and early-80's has a bump-and-run style that was impossible for WRs to beat, and Oakland nearly hospitalized Lynn Swann on more than one occasion. Those '85 Bears in the modern NFL would be suspended for hits and likely been banned from whole seasons. So too would LT!
Since the 2000's, the league has been much more about passing and big plays and bigger contracts to the QBs, WRs and LTs. The Greatest Show on Turf AND Payton Manning's Indianapolis Colts both ran afoul of Bill Belichicks' Patriots in that early 00's era - which directly led to the rules changes that completed the shift from running and defense (mainly) to throwing and offense (currently). The introduction of "illegal contact" as a defensive penalty came after the 2001 Rams and the 2002-2003 Colts were man-handled in Super Bowl and AFC Championship play. The 5-yard plus automatic first down for contacting a WR or TE or RB more than 5 yards down field made it far more difficult to play defense. The 2001 Baltimore Ravens were an all-time great unit, but even they fell victim to the shifting tides by mid-decade.
Seattle's No Fly Zone defense was another tough unit, but the Legion of Boom was undone by Pete Carroll's allergy to using his best running back at crucial moments of championship games. He is the only coach I am aware of that managed to lose both a college BCS title game (2005 Rose Bowl versus Texas) AND a Super Bowl (2014 New England - Seattle first time) by NOT handing the ball to his best player to get ONE YARD that would have won both games. In college, he took Reggie Bush off the field and handed the ball to LenDale White, who got stuffed on 4th and 1 and turned the ball over to Vince Young and the Texas offense to win the game... Then in the Super Bowl, he had the ball 36 inches from the game winning TD and instead of handing the ball to Marshawn "Beast Mode" Lynch... he dialed up a pass that was intercepted and cost that great Seattle defense a ton of long-term respect and memory as one-time champions instead of back-to-back...
The last 15 years have not seen very dominant defenses and while the 2025 Seahawks were good, they benefit from both recency bias (LAST NIGHT!) and an inferior opponent playing a really bad game as well. Their pass rush - especially getting pressures with a 4-man rush instead of heavy blitzing or scheming - was elite. Everything else was just solid and good for sure, but not legendary or on par with even the Legion of Boom / No Fly Zone Seahawks team.
I think years from now, this year's Seahawks will be recognized as a very good team, with some elite talent and traits, but not anywhere near the levels of the past; HOWEVER - given the focus of the rules (can't hit WRs over the middle, can't BREATHE on QBs, offense gets away with a lot more holding as well) and the changing emphasis on the passing game, those great units from early eras might struggle as well!
I hate the Patriots - mainly because they beat the then St. Louis Rams back in SB36 as 14-point underdogs, and set off a negative feedback loop that ended with the Rams and the NFL leaving St. Louis in 2015 for L.A., but also because Robert Kraft is an entilted billionaire bitch-boy and a disgusting person, as well as a Trumper..
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certainly the best in a Steelers history. 
