We are leaving a cruise at the port to Rome. We are then taking the train to Pompeii then on to Sorrento for two nights. We want to store most of our luggage at either the Fiumicino airport or the Termini train station. Is one location more secure than the other or should we base our choice completely on convenience? After Sorrento, we take the train back to Rome for an early morning flight home the next day. Thanks for your suggestions on these last logistic details. We haven't stored luggage before, are there details we need to know that you can suggest?
First thing is to find out the opening times for the Deposito Bagagli. I would leave luggage at Roma Termini and pick it up before your last night in Rome in case you need to get to the airport before you can retrieve your luggage.
See prices for Roma Termini at http://www.romatermini.com/en/service/detail/left-luggage. You might pay 25-30 euros per bag to leave them for 2 - 3 days (which is what I expected, that location is not cheap). This office has told me in the past that they only accept locked bags.