From Nice to Aix, if you don't mind curvy roads I'd recommend driving by the hinterland :
- follow the Route Napoléon to Castellane, with many possibilities to sidetrack in some remote and even quite wild places after St Vallier (the first pass),
- then veer left in Castellane and drive down the Gorges du Verdon (in La Palud, taking the Route des Gorges (D23) certainly won't make the trip shorter, but it can be nice if it's not too crowded),
- then follow through Moustiers (Lac de Ste Croix), Valensole (lavender fields), Manosque,
- then cross the Luberon driving through Apt (many scenic places ; the old "carrières d'Ocre" in Rustrel are nicknamed "le Colorado Provençal" with the characteristic sense of understatement of the people of southern France ; avoid Gordes if you don't particularly like crowds, I prefer Murs eg).
Around Aix and Avignon, the Ste Victoire is a pictorial must, but don't miss the Alpilles (St Rémy, Eygalière, Mouriès, Les Baux - preferred vineyard Mas Ste Berthe near Les Baux), the Dentelles de Montmirail (north of Carpentras, many vineyards too in Gigondas and Vacqueyras), around the Ventoux (Montbrun, Gorges de la Nesque...) and there are still many other nice places.
If you got some time, a day walking in the Calanques near Marseille can be very rewarding too. I'd recommend going to Sugiton and the Devenson from the Luminy university but there are many other possibilities - if you don't want to walk, you can also drive through Marseille to Les Goudes at the west end of the Calanques.