Maui...hands down.
You've got warm water all year, lots of large pelagics, Manta Rays, thousands of reef sharks, tiger sharks, dolphins, one of the largest endemic populations of small invertebrates in the world. In the winter months humpbacks migrate thru there. Massive fields of coral and all that brings. One dive off Lanai, the DM estimated there were 5000+ Moorish Idols, an equal number of tangs/butterflies and I personally counted 12 different white or blacktip sharks patrolling the edges of the school. That's normal there - there's a site we didn't get to that's described as even fishier.
There's shore diving along the entire west Maui coast - even a couple places on the east side. Molokini crater is 15mins. by boat from South Maui - it has both the easier crater diving and the more advanced 300' vertical backwall. All of this reachable by owned private boats ranging from large zodiacs to 40-50 power cruisers - nothing more is needed. The south Maui (Kihei) shops all launch theirs from the Kihei boat ramp so although big, still trailerable.
There's also diving around most of the island of Lanai - about 20-30mins off West Maui. The Cathedrals are a complex of lava tubes in that area that are fully rec. diveable.
Plus bluewater Hammerhead diving off Molokai - about an hour ride out. There's even a few small WWII wrecks off south Maui, a bomber and a landing craft. Plus the deliberately sunk Carpathian and a couple more I can't recall. You can dive with Tigers off Olawalu regularly, or do much easier and shallower diving along much of West Maui, either by boat or from shore. Nice thing is a lot of the sites are also very nice beaches so entries are easy and non-divers have things to do also.
So in effect within an hour of Maui, you can dive 3 other islands that are all very different in nature. I haven't been to Molokai but a lot of Lanai diving is extremely vertical - as is the island itself. Yet off Maui the shore diving is typically shallow for a very long way out, to get to deeper reefs we use scooters.
We rent an excessively overpriced condo in the Wailea area. One draw for us is walk thru the parkway in the middle a few hundred yards and strap on the gear and dive the north end of Wailea Beach, a named dive site. With 5 others within a mile drive. It's very good diving, puffers, triggers, endemic reef fish, one trigger only lives in Wailea bay and one other area. Lots of coral also - off Lanai in a few places it limits access to the beach since it's so thick and shallow - at low tide you can see it. Many of the dive shops offer fill cards for shore diving, most also off Kaimana (sp) rates when you live there.
On top of that Oahu, Kauai or the Big Island are an hour flight away.
Oahu has some WWII wrecks legally diveable plus some shore dives. As well as excellent boat diving - I understand there's one dive you can do near the fish farms with an extraordinary number of sharks around - it was on CBS news once.
Kauai has less in shore dive options but Ni'ihau Island - an all day trip - has arguably two of the more spectacular Hawaii dives, Vertical Awareness and Keyhole. Plus at least two dozen boat dives done via local boats. In summer months Tunnels Beach is a series of rec-level explorable lava tubes. Sheraton Caverns is acres of the same - mostly collapsed. Huge green sea turtles live there.
On Kona you've got the world famous Kona Manta Dive. It's 12th on one of the better best of lists. Also in south Kona your "buddy" is occasionally 100 spinner dolphins. The Kona Aggressor also works the area farther south than the dayboats roam due to timing/fuel issues - none of them are big boats.
I've only been diving two places in my life where I've seen regular people get off work and drive to the beach to go dive b4 dinner. Maui and LaJolla (San Diego). I don't think that's as possible on the other Hawaiian islands either - except maybe Kona since a lot of people live on the south Kona coast intermixed with a few shore dive locations.
Obviously it's possible in SoFL also, one of our ex-staff members dove from her condo's "sideyard" near Ft. Lauderdale. SoFl airports - both MIA and FLL - have a large amount of flights to excellent dive locations like the Bahamas out islands, ABC's, Bay Islands etc.
Most of the time when we route to a Caribbean destination it's thru one or the other. Plus there's some regional hub connections into the Virgin Islands or Puerto Rico. PR is a hub for many of the Southeastern Antilles - once there we heard flights called for 1/2 dozen known dive destinations - places like St. Kitts or Dominica etc. - our flight was thru MIA first.
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