2014: Michigan was the winningest (by percentage):

https://web.archive.org/web/20130830063602/http://www.winsipedia.com/ran...

Earlier this year, they were 3rd:

https://web.archive.org/web/20201006090022/http://www.winsipedia.com/ran...

With this loss, they dropped to 5th:

http://www.winsipedia.com/ranking/all-time-record

I think Ohio State could take the number one spot by the end of the year!