When traveling long distances in Europe and the UK, I typically take the train when possible; however, to enjoy the countryside and smaller villages, I prefer to rent an auto. Obviously, there are many companies from which to choose, and some prefer Autocar.com, which often affords lower prices, but I seldom use this agency.
Over 40 years of travel, I've tried Hertz, Avis, Amoco, National, etc., but when became Hertz Gold member, I've stayed with them, even though their prices sometimes are a bit higher. I like the amenities that Hertz offers, including periodic savings on navigation systems, multiple-day rentals, etc.
Since you can't pay for a car rental with cash, I use either my Visa or American Express charge cards to cover the expenses, and they both afford insurance benefits in international rentals; therefore, I decline the extra insurance charges offered by the car rental companies.
As a word of advice, when renting in Italy, "theft protection" is NOT an option, but even though your credit card might cover other expenses, I've found it best to "prepay" the card to minimize the potential damage deduction (from 1,900 Euros to 300 Euros). If you have to cancel the rental before arriving, your charges will be reverted.
Regarding credit cards and car rentals, it's best - perhaps mandatory - to post your credit cards on the respective rental car websites, listing your priority for payment.
Regarding portable, navigation devices offered by the rental companies, I'd suggest removing these from your auto when you leave the auto, at hotel check in, for instance. * Don't leave them in front seat pocket, trunk, or especially, visible inside auto! Also, before you accept extra charges for a navigation device ask if there's an extra charge for this if you return the auto to a different location than where you picked up the auto, as often these devices are owned by the rental office.
One other precaution: Before leaving the rental office I always check the gas tank to insure it is full and check around the auto (particularly the side mirrors) and advise the office of any scratches, dents, etc., and have them mark them on the rental agreement, or you're perhaps liable for them when you return the auto.
PRECAUTION: Don't think that your parking, or other fines, will not find you out when you return home; they will likely be sent to the rental office where your rental records are on file!