My wife and I recently spent 5 nights at the JW Marriott Ko Olina on Oahu. Wonderful spa right across the street (w/tons of exercise equipment and a great lap pool), wonderful uncrowded beaches. Recommend staying before Aug 11 as that's when the mega-Disney hotel and timeshares open right next to it.
I could not love a resort more than the Marriott Waikoloa. All the families with kids seem to head to the monstrous Hilton up the road. The Marriott is peaceful and beautiful. The spa is not as luxurious as others, but the experience is great.