Hi Peter,
This trip or mine should get you oriented:
"You will not find much nice coral off any of the Hawaiian Islands ala the Caribbean. Only small patches of relatively colorless stuff. Also, sparse sponge or vegetation for the most part. Look for relatively cool water temps, like 77 plus/minus 2 degrees, and modest viz, like 40-80'. Marine life is another matter altogether. Varieties of butteryflyfish, triggerfish, surgeon/doctorfish, etc. far out number those found in the Caribbean. Also, lots of turtles.
If this is your first dive trip to Hawaii you might want to read "Hawaii Below" by Rod Canham ISBN 0-922769-21-4. It is a pretty good book covering all the islands and most of their dive sites, another good book is "Shore Fishes of Hawaii" by John E. Randall ISBN 0-939560-22-4. These are probably both in out of print status, so be prepared to order that way.
The Big Island has a wide variety of topography & excellent diving of the Kona coast. It is my first choice. Neat manta ray night dive -- the one at the now closed Kona Surf used to be almost guaranteed, but longer so. Action now is a bit north to Eel Garden Cove. Some excellent shops, including Dive Makai, Sandwich Isle Divers, Aloha Divers & Jack's Diving Locker, although these draw experienced divers. The less advanced might want to check out Eco-Adventures. Don't miss Volcanoes National Park, rain forest outside of Hilo, or the coffee plantations. Roy's on Big Island, too. Have drinks at the Mauna Lani, near the Orchid (nee Ritz-Carlton). Kevin Costner stayed in one of the 4,000 sq.' villas with a Mercedes sedan and valet while filming "Waterworld" -- you'll know why it ran so much over budget.
For diving in general & shore diving in particular, check out web sites of Big Island Divers, Kona Coast Divers (but don't dive with this op) and Dick The Diver. Also do Phosphorescent Bay at night. Sharon's Place, Long Lava Tube, Hammerhead Point & Golden Arches also good. Can do shark cage dive with Hawaiian Divers. My favorite shore dive & an easy one is Place of Refuge you will nice coral here. If diving with EcoAdventures, be sure to do the "Toilet Bowl" -- really fun. Eat at Cafe Pesto, Donatoni's and La Bourgoyne. You won't be sorry.
Maui would be my 2nd choice. Depends really on where you are staying because Maui is like two islands: south side which has Kehei, Weilea, and Makena - with some good shore diving and located close enough to the Molokini preserve. Diving out of West Maui, meaning Lahaina, Kaanapali, Kapalua, etc., usually indicates that the diving will be by boat and off to the island of Lanai, meaning Cathedrals #1 and #2, Monolith, Sergeant Major and even Turtle Haven. There is some shore diving that is available. Mike Severns has equipment and dives out of Kehei boat ramp and is the operation that has the greatest knowledge of Molokini - both he and his wife are biologists and have the definitive coffee table book. Out of Lahaina, the Mala Wharf, is Erik Stein's Extended Horizons and they also supply good equipment. Both of these are charters, and do not have stores. Lahaina Divers is a safe operation that caters to the walk-in trade and a good cattle boat op. Day trips to Lanai good, but Molokini Crater way over rated -- it's snorkel & scuba central & shows the wear & tear. Back side can be good, weather permitting, but is for experienced divers only due to depth, current & often rough surface conditions. Ed Robinson's also a very good dive op. On the north shore of Maui at Nakalele Point (where the lighthouse is) there is a wall which plummets over 120' straight down (might go more but that's as far as I've gone). I admit that it is a very tough climb down and then back up the lava cliffs, and that it is a very physical dive, but the wall is still there for the hardy (mountain-goat types). As to the coral situation, there are two very colorful areas with literally many (perhaps hundreds of) acres within easy shore diving distance. One is right along the road to Lahaina at Olawalu. The other is on the north side about 3 miles past Kapalua. It is a marine preserve called Honolua Bay. Describing shore dives; also purchase the small paperback for about $10, "Divers Guide to Maui." Eat at Roy's (creative pan-Asian cuisine & not inexpensive), Nicholina's, Sam Choy's, Longhi's (big splurge) & Stella's Blues Cafe (organic).
My 3rd choice, Kauai, is prettiest of the islands, and has one of the best shops, Bubbles Below (
www.aloha.net/~kaimanu/), located off Nawiliwili. Linda, co-owner & DM, is the most knowledgeable & enthusiastic marine biologist I have met. Great educational lectures during surface intervals. On one trip she pulled out a box of crab claws & demonstrated what the features of the claws told one about the life of the particular species. She knows where the rare stuff is, like boarfish & Hawaiian morwong. Los of turtles at Sheraton Caves & Sheraton Tunnels. Do the 3 tank dive trip to Niihau if you are an experienced diver & they are running it (long boat ride & very weather dependent)--several spectacular walls that go down well over 200'.
Don't miss the Na Pali coast (featured in opening scenes of sequel to sequel of "Jurassic Park," "Lost World") in the far north, dinner at Roy's & A Pacific Cafe (both expensive but unique & worth it; creative pan-Asian cuisine), and a drink at sunset at the Princeville Hotel (talk about "Lifestyles of the Rich & Famous"). Northern coast is rainiest, southern coast (Poipu) is sunniest. Can stay in middle around Kapaa & do both. Outrigger Resort is quite nice for the price, although beach is just so so. Think about doing a helicopter tour of the island if the weather is good -- worth the cost. Nice golf courses at Princeville & Marriott resorts.
Take adequate thermal protection. To dive at high season with any of the ops I mentioned, book well in advance."
Happy choosing.
DocVikingo