I don't understand the John Harbaugh love. I'm not going to disparage him, he won a Super Bowl and that's big, but college is a whole different animal. He'd be a risk IMO whereas the others are more proven as far as college goes.
My thought process:
He grew up around the college game
He coached college ball for years.
He won a Super Bowl.
His teams are always fundamentally sound.
He's taken some decent teams that got off to really bad starts, faced the adversity, rallied the troops, made the necessary adjustments and brought them back to the top ... all in the same season . He's done that mulitiple times in his career.
I don't think he's ever had a truly elite quarterback, yet, he still wins.
He will spread you out on offense and still hit you in the mouth with a sound running game (in most years)
He typcially fields a stout defense.
He is intense but a players coach.
2 things we know about bloodlines:
If your last name is Manning, you can QB.
If your last name is Harbaugh, you can coach.