Being a beef fan I had heard from some people that Johnnie's had the best Beef in Chicago.  I will admit it is damn good.  However, it is rather on the small side and a bit expensive.  I can't say the place is bad but if you want a better beef go to Duke's drive inn in Bridgeview Il.  Great beef sandwich and it takes 2 hands to eat it.
Pros:  Tasty
Cons:  Small, Pricey
                        
more