There's only one liveaboard, the Kona Aggressor. But again they're SSI not PADI. It's been called the cellphone liveaboard since you're rarely out of range except at the far south end, I think a lot of what they dive you could do off dayboats - except that it might be cheaper - Kona isn't the cheapest area for accommodations or dive prices. The only place to night dive with Manta's is off the Kona coast on the Big Island - Hawaii. My buddy had a real good experience last year with Kona Diving Co. friscuba (Steve) on the board here owns another dive operation in that area.
There's also Manta's often spotted off Maui. My buddy dove with Ed Robinson's out of Kihei and they went to a cleaning station just offshore and saw 3. But they couldn't get too close. Off Kona at night they may knock you over during the night dive. At least their wake will, they rarely touch anyone. Wreck diver might be a little difficult off anywhere but Oahu - but IDK for sure. There are a couple of recreational depth wrecks off Maui but not really what I would think would qualify for a wreck diver specialty - we dove them as OW divers. On Maui you either stay in South Maui - the Kihei area - and dive with an operator based from the boat ramp there or stay in Kanaapali/Lahaina and dive with an operator there - it's a 45min. drive between the two areas. Often recommended here are Ed Robinsons, B&B Scuba and Mike Severns in south Maui - Lahaina Divers and Extended Horizons in West Maui. But there's others.
Turtles are everywhere, I've seen lots of them off Maui - they sleep on one of the wrecks just offshore and there's big turtles at Sheraton Caverns off south Kauai. There's so many turtles at Kahuluu Beach Park on the Big Island that it's known for that. It's also a snorkel as it's only about 7-10' deep for a long way out.
Dive operators to look at on Kauai are Seasport Divers or Fathom Five. I dove with Seasport and recommend them occasionally here. If you're planning a trip soon the north shore of Kauai will be blown out (big waves) for about another month or so. So stay/dive in the south around the Poipu area.
