My top 3:
1. Dye
2. Shug
3. Hear me out before you criticize this one… Gus.
I think the first two speak for themselves. As for Gus… He was fizzling out before he was let go. Partially, it to a fall off in recruiting after Kirby was hired. But he also was a little stagnant at times in letting his offense evolve. (Albeit, I feel like he gets a little more flack on this than is realistic. He did make some changes to his passing game, especially after Chip Lindsey was hired.) And his last few years, he was over-substituting, which tended to telegraph what play we were about to call.
HOWEVER, he put a ton of guys in the NFL. He ran a clean program that kept players from getting into too much trouble. Including his OC years, he had us on 3 SEC championships and 2 natties within a decade. His win percentage was on par with other great Auburn coaches. He had a pretty even record against Saban. And oh yeah, he did all this with our biggest rivals(s) having unprecedented success.