Train from Florence to Venice

If your itinerary is set, why not save money and buy nonrefundable tickets now? If you buy at the station, you will pay the maximum price. Assuming you are not immediately coming off an airplane.

Trenitalia is run by the state and .Italo is a private company other than that they use the same tracks and have pretty equivalent trains. Some people had opinions about seats or comfort but for a trip as short as Florence to Venice I don't see any real difference. Since .Italo is a private company they tend to be less affected by strikes but this is an edge case to decide which company to use versus time of day, price etc. which should mostly drive your decision.

Fast trains between big cities and these come with assigned seats on a specific train and tickets can be purchased early at a (sometimes sizable) discount but come with restrictions. The earlier you buy the cheaper the tickets but you're trading economy for flexibility. If you buy the cheapest tickets and miss your train you are out of luck, but if you are generally sure of your schedule the savings are enough that most people decided to buy earlier if they can. Generally all the options for discounts are good deals - read the fine print and as long as you qualify it applies - except for senior discounts on Trenitalia which you need their special card to access and is notoriously difficult to get in the states. Tickets for fast trains are generally available two months ahead.

Many people report having an easier experience in English on the .Italo site versus Trenitalia where you generally need to use the Italian names for places - Roma, Firenze, Venezia etc. Get used to using 24 hour "military" time when dealing with trains but it's used less in Italy outside of trains.

The man in seat 61 is a really good basic primer on European train travel: https://www.seat61.com/train-travel-in-italy.htm

Have a great trip,
=Tod