Our previous experience of Europe led us to be in favor of the train. So we planned to go from Naples to Rome on the fast Eurostar.
We waited until the last minute on Sunday to go to get tickets, and the 7:30 Eurostar was full, so we ended up on the 8:30 one. We got our tickets and picked up a roll and some cappuccino in a bar in the station while we waited.
Despite the jokes about the trains in Rome, this train came and left on time. We of course had seat reservations (these are mandatory and part of the price of any of the high speed trains in Europe, not only the Eurostars but also the TGV.
We had no problem finding our car on the train, settled into our seats, and within two hours we went from central Naples to Central Rome, nonstop, in great comfort.
At about 20 Euro for the whole trip it seemed a bargain.