Citivavecchia to Paris

It all depends upon your definition of "best." If you want convenience and aren't worried about expense, take a private shuttle (over €100) from Civitavecchia to either Fiumicino or Ciampino and fly to Paris. Or take a train to Rome for a few euros and either a train or bus to the airport of your choice.

For budget airlines, your best choices are Fiumicino-CDG on Vueling or Ciampino-Orly on easyJet. Ryanair flies Ciampino-Beauvais, but Beauvais is a long way from Paris.

Or spend a few hours in Rome after your ship docks and take the direct night train from Rome to Paris. No hotel bill and a relaxing ride.