Had to argue with drunk Nebraska fans who brought up their 90's defenses. While I think they were great. I say Alabama 92. And I mean defenses you actually watched. I don't think they allowed more than 200 ypg. And under 10ppg
Me seeing and watching personally would be the 2008 USC Trojans. 12-1 record with 9.0 points against per game. The one loss was the annual meltdown against an inferior team in this case Oregon State. (college ball only)
They weren't the best defense I've ever seen, but the 2004 ISU defense was a fun of a defense to watch as I've ever seen. That KSU game was a thing of beauty.