To get to Sardinia you basically have two choices: by plane or swimming.
Joke.. plane or ship.
In Sardinia there are two airports that work all year round and they are Cagliari (the capital) and Olbia. In addition to these two there is a third airport which is that of Alghero, which however is practically closed during the low season or in any case offers few flights and for few destinations. All three airports offer car rental services, but clearly Cagliari and Olbia have more cars available.
The main airport of Sardinia is Cagliari.
Where to land essentially depends on two factors: where it is convenient for you economically (also consider the cost of car rental) and where you want to go. It makes no sense to save 100 euros on flights if you then have to cross the whole of Sardinia by car. Keep in mind that it is quite a long region, so from north to south you will have to drive about 3 and a half hours.
Unless you find a super offer at a bargain price, I suggest you book a flight at the airport closest to your destination.
The main ports are: Porto Torres (north-west), Olbia and Golfo Aranci (close to each other and located in the north-east) and Cagliari. There are also some ferries that arrive in Arbatax but let’s focus on the four main ports which are the ones I have listed.
Based on your port of departure, the port of arrival will change. It is unlikely that you will take a ferry from Nice or Genoa to Cagliari. They exist, but they are such long journeys that I would not recommend them to anyone. It’s much better at that point to arrive at one of the northern ports, stretch your legs and then tackle the journey by car.
The ports of Golfo Aranci and Olbia are very close to each other, about 20 minutes away by car. Most ferries from Italy arrive here.
The companies that carry out maritime transport are more or less these: Tirrenia, GNV (Grandi Navi Veloci), Sardinia Ferries, Moby and Grimaldi.
Each company has its own characteristics and strengths. Some are more pet friendly, while others have areas dedicated to children.
Do you want to know from me which one is the best? They all suck equally in my opinion. It is a poorly controlled sector and especially during the high season they do what they want, with absurd prices for damp and claustrophobic rooms. But anyhow, the important thing is that you arrive at your destination and allow us to reach that paradise that is Sardinia as soon as possible.