I'm originally from Brooklyn and now live in Chicago. I spent 15 years in Pittsburgh so believe me when I tell you that this tiny crowded little unassuming shop has the best pizza in Pittsburgh. It's the best I've ever had outside of New York and New Jersey. I ate here up to 4 times a week and when my wife and I visit Pittsburgh it is one of the first places we go. Get a simple slice - you can get toppings but you don't need them. The crust is incredible and the slices are massive.
If you go and see the elderly Italian gentleman sitting behind the counter say this to him: "Mr. Scott says hello." His face will light up. You probably won't get free pizza but you'll see just how personal the place is.
If you aren't in the mood for pizza, all of the hot subs are great as are the huge calzones - again, it's that crust!
If someone tells you Mineo's is the best in Pittsburgh, thank him or her and then head to the corner of North Craig and Bayard in Oakland to Pizza Prima. Mineo's is good, Pizza Prima is amazing.