Which train ticket website?

Italiarail is an US ticket agent for Trenitalia. Try the same journey on both sites, and you'll see whether Italiarail is more expensive then Trenitalia. Personally I have good experiences with Trenitalia. Easy to use* and reliable.
*) There is one thing to pay attention to: although they have an English-language button, you still have to fill out the station names in their Italian originals. It doesn't understand »Venice«, but is most obedient when you order »Venezia«.

Italiarail charges a small service fee at the end of the transaction. Since they now appear to no longer do transactions in euro, you also lose a small amount in the currency conversion. They may be a bit more user-friendly for credit card transactions.

The trenitalia website is very easy to manage, but honestly I buy most of my tickets at the kiosks (not the window) of the train stations.

For longer journeys on the fast Frecce trains advance reservation can get one considerable discounts.
For the »Regionale« trains it makes indeed no difference. And I must say in honour of the FS that their ticket machines are one of the best I know. Clear. Flexible. Perfect to look up a journey. Take cash. Never had any problems with them.

Some people have trouble getting their credit card accepted by Trenitalia. This happened to our daughter a few days ago, using a Chase Visa card. She finally got the transaction to go through using Paypal instead.

You can now also book Trenitalia trains with Captain Train (formerly Capitaine Train), which I have not used but is reported to be easy for US customers: https://www.captaintrain.com/#

Thanks for all the input. Will do a little surfing between the two and let you know my findings.
Thanks for sharing your experiences.

Texasbiggs

As Harold mentioned, you can also book tickets on both Trenitalia and Italo using www.capitainetrain.com. I've used it on a number of occasions and it is indeed very easy to use. If your trip involves rail travel in several countries, they also sell tickets for German, French and other rail networks. Before purchase of tickets, it's necessary to register on their website, but that's very easy and just involves an E-mail address and password.

Thanks for all the input. It is very nice hearing from the travel Pros.

We just returned from 3weeks in Italy and used Italo website at 120days out for the best price. We found it very comparable to Trenitalia (price, schedule, they used the same stations - Rome Termini, Florence SMN, Napoli C) - we had NO issues booking and paying and printing tickets straight from the Italo website - and you can see seat/class differences before you book. We were VERY pleased and will use them again.

Has anyone purchased train tickets for Italy here on Steve's website (RailEurope) rather than directly through Trenitalia? Do you pay a little extra? We are planning to stay in Venice, Florence and Rome next May before a Med cruise and train between the cities.

Thanks.

Regarding Trenitalia, someone said it's easy and reliable. Having traveled Italy for about 5 days with train this October, I beg to differ. When I tried to buy tickets, Trenitalia website at an occasion would show there are seats available, but when I click on purchase, it would say no more available seats. Simply Trenitalia website usage was not intuitive - I have used Amtrak, Greyhound, expedia.com, kayak.com, etc websites for ticket purchases but Trenitalia was the least intuitive for me to use.

Speaking of Italian train, our train from Monterrosso Al Mare in Cinque Terre to Pisa Centrale was scheduled for 9:05AM this past October. Wife and I strolled to train station way early - let's savor last minutes in Cinque Terre. My gosh, the display panel showed it would arrive at 8:45AM so we rushed to platform 3 - it arrived at around 8:50AM and left I guess no later than 8:55AM!!!