2000 Defense was the fastest defense. Fastest everything actually. You had at least 3 backs and a QB who all ran at least in the 4.5-4.4 range, I believe alcoachamp might've been flirting with that 4.3 range.
Most talented defense had to have been the '05 squad. Two of the best DE's in the country with Warren and Sykes, a D1 LB in Lindsey, and Sommer was one of the best in his class at corner. Add Love, Hicks, White, Lanxter, Walker, etc...
'08 was my favorite. Beside T-Rob off the edge, really no huge stars. Sam Thompson led that defense, and was one of the smartest players to come through Alcoa. Such a great safety!
'89, '01, '06-'10, and '12-present have all had great defenses, it's really hard to choose. As long as Nix is calling the shots well always have a great defense.