Maui is more of a night life party scene, the kids might like that. Plenty to do above water for a few days. Molokini crater is way over rated IMHO, the back wall and reef ends are world class. Kona side is not so much into the night life but it has great shore diving. Owning a boat there, I still shore dove most of the time. It also has the manta dive and blackwater dive. Many more days of top side adventures on the big Isle too. Sorry Lisa but Oahu just kinda sucks. Just got back today from my first trip to Kauai. Nice island but not so great if diving is you foucs.
If your into quiet and laid back, Big Isle, if you want shopping and bar hopping, Maui. You wont go wrong either way.