Trains

Trenitalia has many more runs and the top speed of their fastest trains is higher than Italotreno's. Trenitalia's Freccia are a little more spacious and less tilting than Italotreno.

Italo's complimentary wifi works better, the staff is more polite, their walk-up tickets are more flexible and the discount codes they mail every week are unmatched.

I'd just Pick the cheapest train that departs at the best time, both journeys last less than 2 hours.

Thank you,Do they all leave from Termini?

They sure do!

There's not really much difference with high speed trains between the two rail networks, so I'd use the one that provides the best price and the most convenient departure times.

If you choose Trenitalia, you'll likely be using the Frecciarossa on those routes, and both those and the ItaloTreno travel at up to 300 km/h. If for some reason you're on a Frecciargento or Frecciabianca, they travel slightly slower but the time won't be much different in any case. Be sure you're clear on which stations you'll be using as most larger cities have more than one.