Hi, Caymaniac!
I have dived with the following outfits:
Jack's and Sandwich Isle Divers on the Big Island
Lahaina Divers, Maui Dive Shop, Ed Robinson's, and Mike Severns on Maui
Bubbles Below on KAUAI (not Maui)
Jack's is avery professional outfit and I predict you will like them. They take ca. 16 divers on their normal two-tank dives, but divide you into groups of 8, which works out fine. The also have an "Advanced" 3-tank dive that we think is great; on that dive they usually have two groups of 6, a number we prefer. In either case the DM's make certain that the two groups stay out of each others' ways and they make every effort to provide you with a great dive! They also have super snacks and drinks.
Sandwich Isle takes only 6 divers out and we really like their crew, especially Walt. They use the "loose buddy system" and will let you stay down as long as you have air and/or bottom time left. The way they usually do this is to do a guided dive and then return to where you can see the boat after ca. 30-45 min. Since the boat is moored on a nice reef at ca. 30 ft. if you have good air consumption, you can stay down a long time. For u/w photographers who want to do macro, this is wonderful! Their snacks and drinks are a cut below that of Jack's, though!
Oh, yes, Jack's will usually let you stay down if you have air/bottom time left, too.
On Maui the shops that I listed fall into two categories:
(1) Maui Dive Shop and Lahaina Divers have larger boats and more divers. With both shops, if you know the DM and he has confidence in you, they will stay down with you till you are ready to come up. However, in general, we prefer the smaller group approach.
(2) Ed Robinson and Mike Severns take out groups of ca. 12 people and divide the divers into smaller groups of 3 or 4, depending on the kind of dive (and dollars). We love Robinson's boat and his crew and highly recommend them. Severns is a legend among Hawaiin divers, and justly so. He is somewhat demanding, but his wife, who DM's is a real charmer and one hell of a DM. We like Severns' outfit, too. By the way, both Robinson and Severns have written books about undersea life in Hawaii and I can heartily recommend their work.
You mention Bubbles Below: I have dived with Bubbles Below on Kauai and the owner/DM, Linda, is one of the best in the business. However, I am not aware of a Bubbles Below on Maui. If Linda has moved, I would like to know!
We love diving Hawaii and normally go there every year, but it is quite different from the Carib. The most noticeable difference is an almost complete lack of soft corals. However, the hard corals and abundance of wonderful sealife more than makes up for that.
Finally, allow me to make a few dive recommendations: on the Big Island do, by all means, go on Jack's evening Manta Ray Dive; you are almost guaranteed to see 2-8 of the these graceful giants--and Jack's is the best shop to use for Mant dives in my opinion; on Maui, dive the back wall of Molokini; if you have good bottom times and go with Ed Robinson, you can darn near circumnavigate the crater. The sealife there is rich and varied and we always ask to see Turkey Lionfish, if possible. So far, it has been possible on every dive we have made with Robinson on Molokini. But you need good bottom time.
Hope this helps AND have a really great time!
Scorpionfish