I personal like to drive a jeep. With a jeep you can discover the entire island of Aruba. From the flat hotel area to the rocky east coast. With a jeep you do a tour from Baby Beach along the east coast line, through countryside, along the rugged north coast, and then finally you can see the leeward side of Aruba when you return to your Hotel.
If you like a more luxury car like a sedan, a round trip is not possible. In that case you always can hire a jeep for one day to do this trip. Or simply book a trip with Sensitive Hikers. They will show you the Island Aruba Style.
Basically, If you drive from airport to hotel, hotel to Oranjestad en back. You only need a normal car. If you have more intentions like a round trip, you definitely need a 4x4.