Ferentz has done more to date. More major bowls, bigger bowl wins, more seasons in the national title conversation (02,09,15). Both inherited the program in bad shape.
Fry had to build this program from the ground up, change the culture and mentality. For that he will always be a legend. There was not a better coach for Iowa at that time. Fry was tough, innovative, endearing , bullheaded but most of all commuted to the job here.
While there were coaches that could have changed thins here, most would have used the job as a stepping stone.
Hayden put together a legendary staff and build a model of a program.
Hayden brought Ferentz here, mentored him and helped his upward climb.
At the end Hayden left the cupboard here empty. Ferentz came in here and took an undersized, less athletic team and rebuilt it in just a couple of years. He brought a new " lunch pale " carrying, workman like discipline based approach and caught the attention of everyone. He turned skinny QBs into all American LBs and tight ends, running backs into NFL d tackles.
He found toughness and athleticism where he could , coached them and put them in positions where they could become impact playmakers.
He took what Hayden built, revived it with his vision of success, taken it further, and maintained it longer.
This is not a blue blood program in a recruiting hot bed, but it is long term highly successful program. Both coaches are college football hall of fame material in my book.