Purdue more so than Michigan, in my opinion, due to longevity and consistency.
MSU has 73 games with ND, and several with a lot of meaning to them.
Purdue has 83 games, but a little more lopsided in ND's favor.
Michigan has 36 games with ND, but only 7 before 1980.
UW plays them in 2020 and 2021, in NFL stadia. Ugh.