Positano is glamorous -- just as it is in the movies.
I have visited Sorrento twice. I absolutely love it there, it is one of my favourite places in the whole world. I would strongly reccomend anyone to visit Sorrento and the surrounding area, as it is beautiful and the culture is fantastic! I can't wait to go back!
Salerno is definitely less dangerous than Naples. I duly recommend it to use it as a base for touring around the area (1 day in Pompei, 1 day on the Amalfi Coast, 1 day in Capri). Salerno has nothing really special to offer, but is quieter than Naples and from the train station to the hostel is a nice walk. From …
If you are travelling on your own, do ALL you can to avoid staying close to the station - it is an extremely seedy area. The rest of Naples is beautifully chaotic, and feels much safer. Great food and great people.