Train from Venice to Rome (fast Train)

On Trenitalia the fastest trains are 3 hr 45 min. Either the Frecciarossa or Frecciargento. Make sure your departure is Venezia S. Lucia. I used Roma Termini for arrival.

Italotreno is newer, and also has trains, same 3 hr 45 min. I have not been on them yet.

As far as scenery, I have not taken that exact route. I am sure others will answer!

The route is down a flat, main transport corridor with just a bit of scenery. All trains follow the same route, unless you make a very purposeful detour.

Scenery report
Venice to Bologna - boring flatness
Bologna to Florence - tunnels
Florence to Rome - mostly uninteresting in the Tuscany section, in Umbria and Northern Lazio through suggestive and sparsely inhabited country

Ronnie,

The "best and fastest" train is either the Freccia trains (Trenitalia) or Italo Treno. These travel at up to 300 km/h and it's a very easy way to make that trip. Which rail line to choose will be based on cost and how well the departure times work for you. One point to note is that in some cases, Italo trains arrive at Roma Tiburtina station rather than Roma Termini. If you'd prefer to arrive at Termini, then choose Trenitalia.

As these trains have to travel on specially constructed high speed rail lines, there are few options in the route they take. As lachera aptly pointed out, the scenery varies somewhat between different segments of that trip. I've found the best scenery is on the Florence - Rome part.

If you'd like to buy advance tickets, I'd suggest using www.captaintrain.com as they have a very user friendly website. They sell tickets for both rail networks at the same cost as if buying directly from the networks. Note that the fast trains have compulsory seat reservations, which are specific to train, date and departure time, so your tickets can ONLY be used on the ONE train listed on the ticket. Reservations will be provided with the tickets, and will specify a Car no. (Carrozza) and Seat no's (Posti).

Wow what fantastic informative replys. Thank you so much. Will not bother looking for scenery as you all said not much to see but that is ok. Does it matter what train station I arrive at, will be staying near Pantheon, central historic district.

Termini will be your best arrival station heading toward Pantheon.