It varies by year for sure. This year the Big12 is hot garbage, but a few years ago it was fairly tough. The majority of reputable SOS metrics say Iowa SOS was tougher last year. They say ISU's was tougher in '18, Iowa's was tougher in '17 and '16. So basically 3 of the last 4 years Iowa's was tougher.
By what degree? Very small margin if we are being honest. I mean these SOS metrics are all over the place. In the same year you have at least one of the metrics saying the opposite of these results. SOS metrics are pretty much a joke, and resting your hat on them is a complete joke. Yet it seems that is all ISU fans do, so it means so do the Hawk fans here. There is nothing more valuable to a ISU fan than SOS, they can tell themselves just how awesome they could be if they were just somewhere else.