Resurrecting this thread as I do have recent experience of renting from Hertz at FCO.

Renting is fairly easy. My rental was with Auto Europe as agent for Hertz. Hertz would not associate my President's circle membership with the rental either over the phone or at the counter, so I had to wait at the counter for about 20 minutes while all the paperwork was done. It was friendly but not efficient. A big play was made about the damage paperwork, with the two areas being marked as damage showing very minor damage - a level which would be ignored in the USA where I normally rent.

The lot was largely full of Fiat 500s, with a handful of Minis and a very small number of larger vehicles. The Fiat 500 was a fun car to have, but ergonomically terrible and it was not happy at 130km/h on the autostrade. Also, it's gearing was very high, which meant lots of revving was needed to get up steep hills.

Returning at FCO was a nightmare. The first sign for car rental return as you approach the airport was situated shortly after you take a left exit and is very small - so effectively you have to circle the airport and return a different route. It's a good idea to know which parking structure you are aiming for (it's shared with standard airport parking) as, again, the signage is extremely difficult to spot. Finally, after you have taken your ticket to get into the structures, the turn into the one for Hertz is signed extremely discretely, but not with their standard logo so I missed it and had to circle again. When you reach the 5th level, initially there are no Hertz signs, until you have gone to the other side of it, where the first sign appears, again with the non-standard logo.

Chaos ensues inside Hertz's area. There's lots of arm-waving but no directions or help. It seems you have to find a spare space and then go to the returns desk. At the returns desk, the friendly man seemed to be slightly befuddled by the concept of returning cars and there was lots of head scratching, not only for me but also for the people in front of me. Much paperwork followed, with the man having to leave his desk to walk to each car to check it. There was little to no automation, so returns took a long time.

The process from missing the first turn, to reaching check in, took about 45 minutes.