I would highly recommend Kuma's: it's in Chicago.
They are noted for their hamburgers and they are very good. I have been there many times and never a meal.
In addition to the food, the place is not dull. Customers are all kinds, but this is basically a tattooed, biker bar. As far as tattoos and bikes go, I have nothing in common with the crowd and bartenders, yet they make me feel welcome and are friendly yet professional.
If you are into Rewards Network they give miles for United, and I assume others.
www.kumascorner.com