Big-name != best. Williams' marquee defense was a big dud.
Apart from his MNF football prevent defense meltdown against the Cowboys, the Bills' Perry (Percy?) Fewell deserves an honorable mention. He's got a bunch of absolute scrubs out there, and he has them playing good football. That may also have a lot to do with Jauron, though.
The best though is probably Ron Meeks. Colts are getting a lot of bang for their buck from that defense, and their players never seem to do as well elsewhere.