in reguards to Niihua, I have been diving at Niihua for 15 + years, and the company that takes you there is really less important then the exsperience of the captain and quides.What makes Niihua stand out is the sometimes unlimted visabilty,due to no run off on the very dry island.The currents that sweep through although 8 knots or greater
make great drift dives for those exsperienced enough.The best diving there is at Lhu'a rock a cindercone that has a very deep wall on the westside known as "vertical awarness" but personally the drop is over rated, not alot of things on the wall itself,but more going north from the wall. Out off the 100 or so dives at lehu'a the most thrilling dives have been either at"Key Hole" known for a sheer wall drop and it's reputation as a shark nursery. , the other is a pinacle off vertical awareness about 100 yards out from the wall. The blue jacks that are talked about above are some of the smallest of the jack family in Hawaii, the Silver and Black jacks reach sizes wellover a 100 lbs while the blue Amileu tops out around 25. The visablity is what is the attraction
HOWEVER!!! I have seen Species of mammals, fish that are naturally not in Hawaiian waters there, Like White side doplhins(Thahiti),Great Whites(worldwide) Killer Whales and false Killer whales(Alaska) Giant Sunfish, amoung others.
Manta Rays and whale sharks are found in Hawaiin waters all year long and reside in larger numbers in the southern islands(Big Island of Hawaii)