We have always used Stefano's Romecabs when transferring from FCO to Rome, Rome to port, port to Rome and Rome back to FCO. We have always tipped the driver around 10 euros. The drivers have always been very helpful. When meeting at the airport they have always grabbed our luggage cart when escorting us to their car. And when arriving at the hotel they make sure our luggage gets into the hotel. We don't travel light, so we really appreciate the help. And one driver went the extra mile and hunted down a luggage cart for us at the airport when there weren't any nearby.