I'll second the recommendation for Jack's Diving Locker on Kona. They are full service -- set up your gear (if you want), help you put it on, rinse it, take it back to shop at end of day (if you're diving with them again next day)... Nice tuna sandwiches and searching for dolphins and whales during search intervals. Very good naturalist pre-dive briefs on including the hand signals the guide will use to indicate the "special" critters (flame wrasse was my favorite). Apart from safety of their customers, they spend most time and attention helping you find and see the critters you want. Wendy and Keller Laros are local experts on the Mantas (did a documentary) and lead the night dives. The Manta night dives are a must-do! Keller is a total ham, and a lot of fun (if you dive with him enough you will soon know all his jokes by heart).