I wish I had known about Pierino when I worked in South Ken - I got taken there on my last day by some coworkers as my going away lunch, but I had never been there before that. The menu doesn't stand out that much from chain style Italian places, although there are more options and a few original sounding dishes, but the food is far better and the staff are friendly and actually Italian (usually a good sign when in an Italian restaurant).
I'm a big fan of anything they serve with Luganica sausage, particularly the gnocchi. They also make a really great pizza - my father tried to order the pizza margherita and the waitress scolded him for being so boring. That would never happen at Pizza Express. If you want to keep with the Italian theme (and why not?), head a few blocks away to Oddono Gelato for some incredible gelato after your meal.