train from rome to venice

John, either is fine. Whatever works best for desired departure times and ticket price. What website are you using?

Either is fine. Note that some trains leave from Roma Termini and others from Roma Tiburtina. Tiburtina is newer and kind of cool, accessible by Metro or taxi so might be fun to try. I like to use Trainline as they search both lines and show all available discounts on both.

Pick the train for times, price, and departure point. That is only difference. Some think the newer cars on Italo are nicer but they all go to the same place at about the same speed.

They are about the same. I, so far, have used Italo for traveling Rome to Florence and the reverse. I liked the business class premium area for its quiet smaller space with an area to put my suitcase that I can see. I also liked Trenitalia which I took to Bologna for a day trip. Both were comfortable and easy to use. So it might be the times available to transit Rome to Venice that could be a deciding reason to use. Cost is another, Italo seems to have cut its fares as I looked at recently. I did choose Italo again for our trip in 3 weeks, Venice to Florence to Rome again because I liked the Premium business section(smaller quieter).

and if you want to ride in a Ferrari, consider the Italo. It is a bit of a stretch, but the private company which owns Italo is partly owned by some Ferrari senior folk.

Then you can go home and say you went at 320 in a Ferrari!!! That's km/h but you don't have to tell them that of course!!!!