The patriots. They went 16-0 in the regular season in 2008
ANSWER
If you're talking about a single season, the 1972 Miami Dolphins, who went 14-0 in the regular season and won the Super Bowl. (The '08 Patriots went 16-0 in the regular season but lost the Super Bowl.)
All-time, the Cowboys have the best winning percentage among existing teams. Dallas is 467-339-6, for a .579 percentage.
Otto Graham was 57-13-1 in the NFL and 109-17-4 overall, the best winning percentage of all time.
Chicago bears with 697 all time wins as of 10/20/08
The worst NFL record of all time is 0-16, achieved by the Detroit Lions in the 2008 season.
Brett Favre
Among existing teams, the Cowboys have the best winning percentage. As of the beginning of the 2010 season, Dallas is 467-339-6 all-time, for a .579 winning percentage.
Warren Moon, NFL quarterback between 1984-2000, fumbled 161 times during his career and holds the NFL record.
The worst all-time NFL record held by a team in the history of the league is the Tampa Bay Buccaneers' 0-14 season in 1976.
Emmitt Smith 18,355 rushing yards
2009? Broncos Colts Giants Vikings Saints all have 4-0 record
Dallas cowboys
Brett Favre beat Dan Marino's all time passing touchdown record recently.
Rolland Lawrence is the Atlanta Falcons all-time interceptions leader with 39.