My family will be in Rome for a few days. We are planning to take day trip to Naples and Pompeii. Is it better to book a bus tour or just take the train and hire a tour guide there? There are five of us. If we take the train should we take the fast train?
It's best to do whatever you want to do. The Circumvesuviana takes you directly the entrance of Pompeii Scavi where tour guides are plentiful. You can also look at www.toursbylocals.com and choose Pompeii as your destination and see the local guides available as well as their reviews from previous customers.
Ditto to what Tim said. We'd chose to do it independently from Sorrento but we also did a lot of reading before we went, and spent most of the day there. It all depends how happy you normally are with bus tours.
If we take the train should we take the fast train?
From Rome to Naples, yes. From Naples to Pompeii you will be taking a local train (Circumvesuviana) that doesn't have a 'fast train' option although it does have an express option. You will switch trains/stations from Napoli Centrale to Garibaldi (these stations are connected) for the Napoli-sorrento line of the Circumvesuviana, and it'll take roughly 30-35 minutes from Naples.
http://www.eavsrl.it/web/it/content/campania-express-2016-1
http://www.eavsrl.it/web/sites/default/files/eavferro/Napoli%20-%20Sorrento_0.pdf
Be SURE to validate your tickets before boarding the Circumvesuviana; this train is used by oodles of tourists, and fines for being caught with an unvalidated ticket are high.