Olbia in the middle of this area, is a dirty port with big ships/ferries but with a very pleasant, clean and touristic city.

Around Olbia there is a large area with a very beautiful archepelago with lots of nice beaches to drop the anchor. If you prefer to visit a marina, you will be robbed, it’s very expensive indeed!
For instance, per night
Circolo Nautico in Olbia, 78€
Cavallo in Olbia, 125€
Rotondo, just N of Olbia, 205€
Porto Cervo, N of Olbia, 150€ for a mooring buoy

The beaches are wonderful, but on weekends crowded.

To rent an umbrella and sun chair is not cheap