I dive Kona 4 or 5 times a year. I'm told that the coral is not as colorful or as generally impressive in Kona as it is elsewhere (e.g. Coz), but the nektonic life is outstanding. I regularly encounter morays, sea turtles, manta rays, eagle rays, peacock flounders, frog fish, turkey fish, and all manner of nudibranchs. I've seen schools of barracuda, reef sharks, and the occasional octopus. While cruising around in the deep water on surface intervals, it's common to come across dolphins, pilot whales, and the occasional hammerhead. Night diving with manta rays can be totally out of this world.
I don't know what your travel alternatives are, but I wouldn't skip Hawaii.