I haven't dived the Big Island, but I've done Maui a lot.
The Molokini dives are fun and very easy. I have been out with three operators there, B&B, Ed Robinson and Mike Severns. I wouldn't classify any of them as "cattle boats", although they aren't six-packs. B&B does seem to have a few more beginners on the boats than Mike Severns does, but all the ops seem to do a pretty good job of splitting the boat up into groups of relatively similar people. That said, if you are serious photographers and like to sit in one place for quite a while, the dives are unlikely to be paced for you -- and they are all guided.
My husband and I, these days, do primarily shore diving. There are some VERY nice sites to shore dive, with nice facilities and easy entries. Where you go and which shop you use depends on where you stay, but we stay south and use B&B for rentals, and they have gone way out of their way to help us (like the time we forgot our yoke adapters, and they took the valves out of a pair of Al100s and changed them for us!) The Maui Shore Dives book is available at their shop and is an excellent reference, with navigational information for the reefs. We have seen many turtles, and spotted eagle rays, and even a monk seal when shore diving.
Good luck with your decision!