You have stated that you will be on Oahu for part (or all) of your trip. You have 3 days. I have completed approximately 300 of my dives from Oahu, and I'm still discovering new things all of the time there. I don't think, on such a short trip, that I would bother with inter-island flights. Working our way geometrically out from Waikiki, you can walk to the Ala Wai boat harbor, which houses at least one good dive boat, "Cordelia" (HDC). Several other dive boats are based out of Kewalo basin, which is about 2.5 miles from the Waikiki Prince. You could contact Ed at Oahu Travel Divers who can guide you, get you seats on those boats, and show you where the cool stuff is. Either of those two marinas offer easy access to many good dive sites, such as Sea Tiger, Horseshoe Reef, Kewalo Pipe, YO-257 & San Pedro etc. Aaron's in Kailua runs frequent boat dives from east Oahu, and there are two dive shops up in Hawaii Kai, reef pirates and island divers, who go to many of the same east Oahu sites as Aaron's -- corsair, fantasy reef, sea cave if the conditions allow. West Oahu has some of the most beautiful dives but is a long drive from Honolulu -- Underwater Oahu is the only shop on the west side.