When I think good pizza, I think Mercurio's. Seriously, their wood-fired pizza is the best I've ever eaten. I came here often when I lived in Shadyside during college. But now that I live in the South Hills I still make special trips to eat here. In fact, my parents, who are from out of tow, often request to go here when they are visiting.
Whether you go for the classic Margherita or for something more involved like the Capricciosa, you will not be disappointed. I love mushrooms, so my favorite is the funghi, but I try to get something new every time I go. If you're not feeling pizza, they also have delicious paninis. I recommend the caprese or italino.
Many people just go here for the gelato. And it's not wonder why. It's soooo much better than your typical ice cream. They have so many flavors to choose from that picking one is often overwhelming. I try to get something new every time I go.
While Mercurio's may look more like a counter-top service place, it double as a really nice sit-down restaurant. They even offer wine and beer on their menu. Be warned though, there aren't tons of tables, so you'll want to be prepared to wait. Luckily, they do have NoWait, so if the wait is long you can visit surrounding Walnut St. shops while you wait for them to text you your table is ready.
Definitely one of my favorite places to eat in Pittsburgh!