I spent 3 months there for work (I know....rough duty).
Stay in Poipu, on the South side.
Drive up to Hanilai Bay for the day. Snorkle at Tunnels at the end of the road.
Hike the NaPali cliffs. Hike Waiama Canyon. Take a Helicopter tour. The beachs on the south side are awesome.
Watch the sunset at the Sheridan....Awesome....
If you have questions, PM me.
If you do Honolulu, stay at Waikoloa Village (a Hilton property) and swim with the dolphins at Dolphin Quest
Waikoloa also has a private beach....nice hotel
Stay away from Waikiki.....Just like Santa Monica
If you go to the Big Island....do the lava flows at night!