We have been Robinson fans for some time. His boats are large, but he divides the group into subgroups of 3 to 4 divers depending on the amount you are willing to pay. The DM's also give nice briefings prior to the dives, with photos and stories, etc. It is a nice touch.
Maui Dive Shop and Lahaina Divers offer a more "standard" package where you dive with about 7-8 divers.
We have never tired of the outer wall of Molokini. If you have good air consumption, the "loose buddy" system used by Ed Robinson will allow you to go a long way around the wall. And it is worth it! From white tip sharks, to the tiniest of cleaning shrimps, to showy turkey lionfish, to schools of various butterflies, you will see it all. And the hard corals on Molokini are grand.
One thing about Maui diving to remember: the wind frequently comes up in the PM, making an early start somewhat mandatory. Robinson starts his boat trips at 6:30 AM, so plan on getting to bed early! Both Lahaina Divers and MDS both offer early morning dives as well as mid-day dives. The latter will run the risk of a rather rough boat ride and adventurous reboarding of the dive boat.
Oh, yes, Robinson will have coffee for you when you arrive, but I recommend bringing your own...it is not the grande latte that you might be used to!
The Fish Who Only Its Mother Could Love, Scorpionfish