My favorite is the Wailea area of Maui...beautiful beaches and consistently good weather.
We also enjoyed taking a day to do a couple short hikes to waterfalls, black sand beaches, etc. on the road to Hana in Maui. We took the road all the way around, but next time we will turn around before the roads get crazy past Hana. IMO the best sites come prior to that and you can avoid the stressful stretch of road.