Michigan certainly seems to be more selective. The middle 50% of accepted students have considerably higher SAT and ACT scores than does the middle 50% of accepted students at Iowa.
Office of Undergraduate Admissions: About Michigan
SAT Scores for the Big Ten - Compare SAT Scores for the 12 Big Ten Universities
ACT Scores for the Big Ten - Compare ACT Scores for the 12 Big Ten Universities
You'll notice that our 26th percentile of students scores scores lower than the majority of other Big Ten schools, particularly on the SAT.
You'll also notice that the bottom end of our 50% in the ACT is in the bottom 2-4 in each category. The same 3 schools match up or are lower than Iowa (There's never more than one school that's lower): Nebraska, Purdue, and Michigan State.
Meanwhile, Michigan's low-end score (27 composite, 27 English, 25 Math) is second only to Northwestern in each category.
75% of Michigan's students scored a 27 composite or better on their ACT. 75% of Iowa's students scored a 23 composite or better.