FCO to hotel

Cheapest and easiest is not always the same. Easiest will always be a hired driver or at least a taxi. Taxis are fixed at 45 euro. The cheapest will be a bus at 8 Euro to Termini and then probably a taxi. Don't know where your hotel is. The train is in between at 16e plus taxi.

Easiest- taxi/hired driver Hotel may be able to set up a driver

Cheapest- Bus to Termini, then Metro to hotel area. Looks like your hotel is midway between stops. Ask your hotel which stop they recommend

Your hotel is next to the Vatican Museum. I would splurge on a taxi ride (48€ all inclusive).
It's far from the station, so train plus taxi is still going to cost you nearly 30€. If two or more people, the cost is similar.

As several have mentioned, a private car service is by far the easiest. After a long flight, some jet lag, not being familiar with the area, there is nothing better than having a private driver meet you inside the terminal and take you to your hotel. No fending off the independent cabs, waiting in the regular taxi line, or just having a "lost" feeling. It is not the cheapest way, but it is definitely the best. We can not say enough good things about Rome Cabs. It is a private car service (not a cab company) but only cost about 10 Euro more than a regular taxi. We always use them and have always been very pleased. Go to romecabs.com and see what you think. We usually send an email and they answer us with a quote within 24 hours. You do have to pay cash (Euros) and the end of the journey but not in advance.

Just adding that normally I think of hotel's arranging the transportation as something I am paying extra for something I can book myself for cheaper.
I was surprised my hotel quoted me a round trip rate for a private driver meeting me at the luggage area and then picking me up at my desired time from the hotel for the same rate or less than I could book a private driver myself and only a small amount more than waiting in the cue for a taxi.

Either way for Rome, if you are staying near Termini public transit from the airport makes sense if far from Termini than a cab or private driver from the airport direct to your hotel is worth the cost.

I would expect a driver Taxi or Private arranged driver to want cash not credit but don't have to tip like you would in the US for the same service.

I've never had to wait long queues at the taxi stand of Italian airports.

The taxi fares are set so high, that every single taxi driver in town wants to be at the airport taxi stand. There aren't enough customers to fill all the taxi that show up in line at the taxi stand. 25 euro from Florence airport to the city center (4 miles), 50 euro from FCO to the city center (15 miles). Really?? No wonder they don't like Uber's competition.

We are using http://bobslimos.com/, it is costing us 65€ for 6 adults and all of our luggage. This obviously would require a larger vehicle, so if there is only a couple of you then I would venture to guess it would cost less. Obviously, divided by 6 people, you can't beat the price and will enjoy the convenience.

Thanks to all for the responses so far. Booked on Heart of Italy Aug 20 so in light of the information I have received, is there anyone also booked on this trip who would like to share a taxi? It sounds like the easiest way to travel but 48 Euros is more than I want to pay if I am the only one in the taxi.