It's so hard to choose, Italy is such a wonderful country. It really depends on what you are looking for. Naples is incredible. It's real and it's gritty. and it's a bit grimy in parts, but I absolutely loved it. In almost every street you can sit and people watch locals going about their daily business. Many people sit on their front steps with the doors and windows open, chatting and even preparing vegetables! There are mini shrines everywhere.
I had the most amazing wine in Naples, that was bought from a store where we got a pizza to take back to our hotel. I have no idea where it came from because it has no label on the bottle, but it was fantastic - and it cost only a few euros. The pizza was second-to-none too.
If you want to be by the sea, then you cannot go wrong with the Amalfi Coast, it's the most beautiful coastline I have ever seen.