I have never had a reuben at Zingerman's, even though I live only 70 miles away.
Pastrami Joe's Deli, 105 North Jefferson Street, Marshall, Michigan, still has the best reubens that I have eaten. When it first opened, I had one of their reubens. While I know that they also serve other sandwiches, I have never had anything but a reuben there. www.pastramijoes.com
The Ordinary, now known as the Out Of The Ordinary Restaurant, 61 South Van Buren Street, Nashville, Indiana had excellent reubens. I have not eaten there since the name change a couple of years ago, but I hear that the reubens are now open face. www.outoftheo.com