Based on what criteria? lots of ways to make a claim, most wins all time, most titles, most bowl victories, most players punched in the face during game time?
Here's two that should be on the list for consideration.
Saban has never had a team that was put on probation due to his players or his acts as a coach while he at a school. He even went along with the school book scandal players on his team getting suspended before the NCAA got involved. He may bend rules, but he doesnt cheat and the NCAA will back it up with no proof of your statement, ever.
Saban's record actually shows he wins a title once every four - five years on average. and he averages just over 9 wins a year for career stats. The man can coach by anyone's standards.