My husband and I got married this past May, and we went to Kuaui, the oldest island in Hawaii and had a blast. It isn't as commercialized as Oahu is (the tourist island where Honolulu is), and there is a LOT of outdoor things to do! It has the Na Pali Coastline where a bunch of movies were filmed (they even have a bus ride that takes you to all the places where movies were filmed). There is also amazing food - dishes I'd never heard of.
Good luck deciding!