I think Nick Saban and Bear Bryant are both no-brainer choices. But hey we are all going to have some bias there. I personally think there are quite a few other choices for the 3 and 4 slots if you factor in winning %, NC's, and where/what level they coached at during their time. I'll list just 2 for consideration though if we are ONLY going by the quality of on the field accomplishments.
I'm shocked that Tom Osborne isn't in there. 255-49-3 (.836) and 3 NC's. His winning% dwarfs any other D1 coach ever at a major school.
Another name is Woody Hayes (I get WHY he's not) at 238-72-10 (.759) and 5 NC's.
That's 2 guys who's winning% and NC's are more than both Bowden and Eddie Robinson who btw coached at a completely different level (not to completely diminish his accomplishments).... but it's not apples to apples.
Yeah I know Bowden, Paterno (not listed for obvious reasons), and Robinson piled up tons of wins but the first 2 coached 6-7 years longer than CPB with a lower winning % and less titles than He, Osbourne and/or Hayes..... and Robinson coached for 17 years longer than CPB again with a lower winning %.
All-Time Bryant, Saban, Hayes, and Osbourne have the best on the field coaching/results resumes imho. But hey it's a great debate. Robinson and Bowden are definitely better people and ambassadors for the game than Hayes for sure....or Paterno obliviously.
Tom Osborne should be on that list somewhere though I think.