Tessaro's is definitely the best burger you'll find in Pittsburgh. Their sides are also delicious. If you have vegetarian friends that protest, they have vegetable kabobs that are actually really good as well. If you love burgers and you're in Pittsburgh, you'll have to try it out. If you've been but haven't gone back in a while, what are you waiting for?
During peak meal hours, the wait can be about 15-30 minutes. The staff is friendly and helpful - they know that they serve a mean burger, and they are happy to be part of it all.
One warning, be prepared to be stuffed.