We had an easy, smooth experience with Avis in Roma Termini. The location is convenient, they have long hours and they spoke enough English for us to clearly understand what we were paying for.
The only disappointment was that they charged us 10€ extra for chains, PER DAY! The chains are required equipment by law in the winter— there should not be a charge for basic equipment requirements. This is equivalent to charging extra for the reflective triangle that’s required by law...this is ridiculous and I will do whatever I can in the future to avoid this charge. You should not take advantage of people this way.