Both Corsica and Sardinia are fairly remote locations, “hidden” gems of the Mediterranean, a popular vacation spot of the “rich and famous” so if you are a budget traveler do what I did: book your car rental (and hotels) a year in advance. There are only a few car rental agencies to choose from and they only have a small selection and limited amount of cars. Car rentals are not only expensive but they tend to get sold out sooner rather than later so once your plans are firm, reserve a car as soon as you can (most rentals can be cancelled or modified), besides you will have to pay for the car when you pick it up so you got nothing to lose by booking early.
Now, both islands have several car rental locations, the most popular ones are at airports and by ferry terminals so you can pick up a car at any airport and return it at any ferry terminal, which most tourist do. Sardinia is pretty big and roads are scarce between the mountains; the serpentine slows cars and trucks down and nobody likes to get stuck for kilometers (hours). Driving 10 kilometers can take you an hour and a half depending on where you are going, airports and ferry terminals can easily be 2-3 hours away one way with “traffic” so smart tourists don’t like to waste time and gas (which is expensive in Italy) not to mention burning the brake pads. Here people prefer one way drop-offs which cost around $100 in the summer of 2015.
VERY IMPORTANT: Once you rent a car in Sardinia, you can’t take it over to Corsica and vice versa. Even though both countries are members of the European Union and the two islands are literally just a 45 minute ride away from each other, the cars are registered in different countries and different car insurance rules apply. You need to pick up and drop off cars on each island, which is a bit troublesome but at least you save on ferry by only paying for pedestrians.
ANOTHER NOTE: You better have an idea of your road trip prior to your vacation because once you land on Sardinia, you can no longer change your mind and request a different location for a drop off or modify the time of return, especially in case of minivans. Since they only have a limited amount of cars and are probably fully booked in the summer months, they really need the car back on time and wherever you indicated originally. So, I suggest you don’t go with the flow here. Stop thinking with your American head 😉
Remember: When you are in Europe, it is not all about you. People in the travel and hospitality industry earn a full wage unlike in the US where agents earn commission. In Europe most agents don’t care if you are happy or disappointed, they will get paid regardless how you feel, whether you return or not, and the more south you go, the slower the service gets 😉 Did I mention siesta? 😉