I visited Naples in March for work. This was another case where we didn't have much time to sightsee, but what we saw was great! When you visit Naples you have to eat pizza, it's an absolute must. When you eat pizza in Naples, you drink local, light beer, not wine like most people think.
We found "the best" recommended pizza place in downtown Naples near Piazza San Dominico and caught a cab from the base to try it out. I'm convinced that it was the best I've ever had. Hands down.
The restaurant is called "Sorbillo" and it was busy when we arrived around 7pm. I ordered the special with Rocket (aka Arugula), Prosciutto ham, and shaved Parmesan cheese. And a beer. It was really the best I've ever had. Cooked to perfection in the open pizza oven like thousands before.
We visited a few other sites but the pizza was definitely the highlight of my trip.