I hate to interject a little bit of hard statistical analysis into an otherwise very fun thread... but here goes, anyway.
First off, the background. There's this site called www.footballoutsiders.com. What they do is they track EVERY SINGLE PLAY OF EVERY SINGLE GAME for the entire season, and compare that play to league average, adjusted for down, distance, and opposition. If the average run on 1st and 10 against the Chicago Bears when leading by 3 points nets 3 yards, and you run on 1st and 10 against the Chicago Bears when leading by 3 for 9 yards, then that is an "above average" play. Anyway, at the end of the season, they total the results from every play to come up with a value for how well that team played that season.
Remember, these totals are ADJUSTED FOR OPPOSITION, so playing an easy schedule will not inflate your DVOA numbers.
Anyway, first, there's the contention that Atlanta was an inferior team to Minnesota in 1998. That's a fallacy.
See for yourself. Atlanta had a DVOA of 32.5%, compared to Minny's 29.1%. Even more, Atlanta was *MUCH* hotter heading into the playoffs than Minny was (45.9% weighted DVOA compared to Minny's 26.8% weighted DVOA). Regardless, NEITHER of these teams were the best in the NFL that season... and neither was Denver, for that matter. The best team in the NFL that year was... New York Jets (34.5% DVOA, 41.1% weighted DVOA). Also, the 1998 Denver Broncos offense was MUCH stronger than the 1998 Vikings offense, but the Vikings faced the 21st hardest schedule of opposing defenses, and the Broncos faced the 6th hardest schedule of opposing defenses.
Atlanta very much deserved their ticket to the superbowl that season, moreso than did Minnesota.
Anyway, using the Football Outsiders statistical database again, which goes back as far as 1998, the best offenses of the last 8 seasons were...
2004 Indianapolis Colts (38.9% DVOA)
2005 Indianapolis Colts (32.5% DVOA)
1998 Denver Broncos (32.2% DVOA)
2000 St. Louis Rams (31.4% DVOA)
2002 Kansas City Chiefs (29.6% DVOA)
2005 Seattle Seahawks (29.3% DVOA)
2004 Kansas City Chiefs (29.0% DVOA)
2003 Kansas City Chiefs (28.4% DVOA)
2004 Minnesota Vikings (28.0% DVOA)
2000 Indianapolis Colts (27.5% DVOA)
1998 SanFran 49ers (26.4% DVOA)
2001 St. Louis Rams (25.6% DVOA)
1998 Minny Vikings (24.0% DVOA)
The 1999 St. Louis Rams had a "paltry" 18.3% DVOA, mostly because of their pathetic schedule.