Traveling from Venice to Naples

It is a LONG trip. BUT, it goes from city center to city center. You would have to find your way from the centers to/from the airports if you flew. Sometimes it can be cheaper to train when you factor in that extra transport as well.

I have done Salerno to Venice, so I have had a tad longer of a trip, but I didn't even ponder taking a flight when I went.

Getting to the airport is not very convenient in Venice, so I would take the train. Total travel time should be around the same.

Train- we had to make the decision last spring, and if you count all the time used, hotel door to hotel door, the train maybe takes ten minutes longer. Also, you have many more schedule option for the train, have a great trip!

Five hours, maybe six, is when we consider flying. But for most trips the train far more convenient. Just get on and relax is comfortable seats and watch the world go by. A lot of hassle with the airplane.

You really won't save any meaningful time by flying as been mentioned. In addition, a train ticket bought in advance will be cheaper and there is much less hassle. A train trip is far more relaxing in comparison, and you get some views of the Italian countryside as a bonus.

Take the train
Take a picnic

Venice hotel to airport: 1 hour to 1.5 hours depending on hotel location
Check in and security procedures: 1.5 hours
Flight and deplaning: 1.5 hours
Baggage claim and ground transportation to hotel in Naples: 1 hour
TOTAL FLIGHT TIME DOOR TO DOOR: 5+ hours
TRAIN PLUS TRANSFERS FROM/TO STATION: 6+ hours
So flying might save you no more than one hour in total, and is more stressful given the multiple steps.
Take something to keep you occupied for 5 hours on the train (or take a nap)

Another advantage of the train is that you have far more departures to choose from. Both major operators on the route, Italo and Trenitalia, operate this almost hourly. So much easier to plan around.

There are not many flights, and I only see one or two direct flights. So you would probably be looking at flights with a stopover, and these are never going to be faster than a train.

And it is going to be cheaper too.

Also, you can visit the restaurant car for a snack or a drink (nonalcohol if you like, or a coffee). Better yet, pack a picnic to bring along. Want a bit more comfort? Travel business class. Not much more than economy when buy discount tickets far in advance. You don't have to keep your seatbelt fastened the entire trip. You can get up and walk around anytime you like.

Thank you everyone for your help. I had a sneaking suspicion that flying wouldn’t save any time. Thanks for confirming that.

have a good trip...