No. 4: Bill Belichick (New England Head Coach)
I had to include one kind of outside-the-box candidate here. Why not replace the arguable college HC GOAT with the NFL head coaching GOAT? Belichick's future with the New England Patriots is shaky at best, and he has been connected with other NFL openings. The coaching resume for Belichick speaks for itself. 6 Super Bowls, 333 wins, a 31-13 postseason record, the list goes on and on.
However, I'm not sure Belichick coaching collegiately would be the best fit. I don't think his style of communication or team structure would work very well in the modern day of College Football. Just like how Saban wasn't built to be an NFL coach, I don't think Belichick is built to be a college coach.
It just is what it is, however, I still think it's at least a possibility. There's also a connection between Saban and Belichick, as Saban worked under Belichick as his Defensive Coordinator with the Browns from 1991-1995. They both respect each other tremendously.