Many first timers stay on Oahu to experience the PCC, Pearl Harbor, the North Shore, and Honolulu. But Oahu isn't much fun once you've seen those places. If you want to golf and stay in a resort or just be around beauty, Kauai is wonderful. If you just want a resort/beach experience, try Maui. The Big Island has the most variety. It's big but far less crowded than Oahu. It has great beaches, places of interest (including an active volcano), great golf, etc., but it's physically not as beautiful as Kauai. In sum, it depends what you want to do. If you could pull it off, three days on Oahu and then three of four on one of the other islands would be ideal. Have fun!