We've been to St. Maartin 3 times. Twice we rented cars and toured the island (third time only went into Phillipsburg). The island is quite small with many beautiful beaches. The car rental agency is at the end of the pier. Last time we went around clockwise with our first beach stop at Simpson Bay where the airport is. We continued to Marigot (the French capital) for a nice lunch, then on to Orient Beach for some swim time. There are also many other nice little coves you can stop at. If you go to Orient Beach find the Bikini Beach Bar (here is their website: www.bikinibeach.net)
. In fact my goal is to retire, buy the Bikini Beach Bar and spend my life serving rum drinks to tourists! It is a beautiful beach and the bar serves food and drinks. There are also many other places to go. But depending on your desires, cars are not too expensive and touring the island is fun. And as I said you also will have time for the beach.
Enjoy. I love St. Maartin.