Ok, I'm going to break this down into two categories, the best all-time and the best, period. I may discuss alternatives when I do..
Dallas
Best All Time: Roger Staubach
Best I ever saw: Roger Staubach
Alternatives: Emmitt Smith, Bob Lilly, Troy Aikman, Bob Hayes.
In terms of Bob, the HOF may not want him because of the drug rap, but when you redefine how people play football, your impact is pretty obvious.
Philadelphia
Best All Time: Steve Van Buren
Best I saw: Reggie White
Chuck Bednarik can eat my shorts. Steve Van Buren was the best runner in football prior to Jim Brown.
Washington:
Best All Time: Sam Baugh
Best I saw: John Riggins
The "best I saw" category for the Skins is the toughest, because Joe Gibbs had an assembly line of players go through his system. One good player would replace another, but his star has always been the running back that makes it all work. Of all of Gibb's running backs, I respected Riggo the most. If I were a little older, "Best I saw" might be Sonny Jurgenson.
N.Y. Giants:
I'm going to split this team a little differently, since Lawrence Taylor was a physical freak who defined what a "rush linebacker" was. I'm doing this because the most unreal performance I ever saw from a Giants player, pound for pound, was that of Joe Morris, in the two seasons of 1985 and 1986. Joe literally was the difference in 1986. Without him, that team never gets out of the NFC playoffs.
so:
Defense: Lawrence Taylor
Offense: Joe Morris.