The Tag, and assistant coaches (Smith hired for LB, Milus for DB)

Smith's defenses ranked in the 20s every year and never showed much sign of improvement. It was his first and I believe only real coordinator job in the NFL (he was given the title in Miami under Saban, but Will Muschamp was assistant head coach and called the plays, and Saban was reported to be involved in all meetings), and I think he lost his players with some of his cheesy motivational techniques (a picture of the rock of Gibraltar, for instance, was placed on every defensive locker and referenced often).

But, as a LBs coach, he's been close to exceptional. He's fiery, he communicates well overall, and should do(and has done) a very good job of handling another coach's philosophy (which is, of course, a big part of assisting a coordinator). He was very good with the 49ers.
It's harder to get Milus. He's not heavy in experience, he's had some success but hasn't been on good defenses in a while, and his work under Lewis in NY (which was certainly a fair portion Lewis' failing, but Milus has responsibility there as well) isn't the greatest. Granted, players tend to come to a coordinator's defense but I find more promising words on Smith than Milus.

The DL job is a critical opening, and there are still numerous coaches out there. A few I prefer, and have gone over a few times, but there are reasons to see them not working here just as easily as them working here.