Marriott's Grande Ocean
Grande Ocean gets my vote. It's simply the finest resort on Hilton Head Island. Beautiful swimming pools, beachfront location, close to Sea Pines Plantation, close to the shops and restaurants at Coligny Plaza, gorgeous landscaping, elegant Coastal Carolina decor. It really is a great resort.
After Grande Ocean, I would pick Marriott's Surf Watch or Baroney Beach Club. I haven't stayed at those resorts, but I have visited them and they are both very nice. Another resort I have stayed at and enjoyed was Kingston Cove. This resort has detached cottages with three bedrooms and is a great place but doesn't have the amenities of the Marriotts and is not on the beach.
Steve