I think grand cayman as much to do. They have swimming with sting rays, turtle rehab farm, and a dolphin experience. Lots of restaurants and condos.
Aruba, did not feel there was a lot to do but my kids enjoyed the ostrich farm there and we had a lovely dinner on a 'ranch'. At the beach plenty to do, including sailboarding and the one where you sail with a half parachute over the water (kite sailing?). Great snorkeling from the beach as my kids were young then.
Curaçao. Lovely beach, fun little old European town, but really there from the beach we could see and smell the gas refinery. (Sorry, being honest, but the hotel was gorgeous!)
St. Lucia-absolute best Caribbean experience we had at the Jalousie hotel (Hilton then, now a different chain) where you have your own cabin with plunge pool, golf vehicles to pick you up if desired when you go to beach and common facilities. Isolated but sits between two pitons and is an absolutely beautiful location. Snorkeling, kayaking and boating in the bay is perfect. Excursions to other reefs available. Pretty secluded though, but did I say beautiful?
Virgin Islands-also nice. We did day trip over to St. John's.
St. Kitts-plenty to do. Day trip to Nevis and snorkeled off a boat/tour. Beautiful and can drive around the island in one day.
Honestly, you will love any of these islands. If you are looking for a Myrtle Beach, all of these are more laid back BUT offer better beaches, snorkeling, restaurants and overall relaxing experience.