It would very much depend where you were driving.
Autostradas are good fast roads to drive. But if you’re staying in Cefalù and heading west, you would have to drive Viale Regione Siciliana, Palermo’s ring road, and it’s horrific to drive.
The A20 along Sicily’s northern coast is easy driving, as is the A19 towards Caltanissetta-Enna and Catania.
The Madonie roads are mountainous roads, but not overly challenging to drive, and you wouldn’t encounter traffic.
Palermo’s airport is west of the city - If you had a tour operator with offerings in Western Sicily, you could hire the car at the airport and drive the A29 in Western Sicily.
As lupaling said, the SS115 along Sicily’s southern coast is a good road to drive. From Agrigento, take the SS640 to Caltanissetta, and connect to the A19 to Cefalù.
Return the car in Cefalù and take public transport back to the airport in Palermo.
With two weeks for your holiday, you certainly owe yourself a more varied itinerary than just spending the two weeks in Cefalù without a car.
Regards,
Vagabonda