I dive Maui about 4- 5 times a year. While I prefer the diving on the Big Island, Maui is more accessible and technically a bit easier.
I STRONGLY recommend Maui Dreams Dive Co (you can find them at
www.mauidreamsdiveco.com ) they are located in Kihei and focus on Shore Dives -- they do excellent training if you want to pick up an advanced certification or a specialty. They do a nice job with guided dives and will go out with a single diver. Their prices are very reasonable. You can also rent gear, get tanks, and just chat about diving with them. Ask for the internet special and you can do a guided night dive with Teri (she's done hundreds of night dives) for $40.
In terms of boat diving -- I have gone on several of Ed Robinson's charters... for the advanced diver the three tank adventure is a nice one... really makes a day out of diving. The Lanai trip can be a long rough crossing and if visibility is down it loses some of it's appeal. In my opinion, Ed Robinson does a good job of smoothly handling guided dives... usually two groups of 6 divers with a dive master for each group... they do not strongly enforce buddies... so you can stay as long as your air or nitrogen level holds out. Having said that, I would recommend them more for experienced divers... If a newbie diver wants to use Ed Robinsons I would recommend that they choose their 'premier' dives which offer a 4 to 1 ratio. In my opinion, the 6 to 1 ratio does not offer enough support for a new diver.
On Thursday nights, Ed Robinsons does a really classy 2 tank twighlight and night dive... very nice.
Mike Severns is also a first class operation -- has probably the BEST marine life briefings going (though some people complain that they may be too long)
I have heard that ProDiver is also meticulous -- though I have yet to try them.
I have also dived with a small shop called B & B. They are pretty basic, but get the job done (guided boat dives) (I have heard a few complaints about their instruction). Their price is usually a bit more competitive, and they have the advantage (?) of leaving a bit earlier than the others, and thus, returning early still leaving plenty of the day for other activities.
I have NOT been impressed with Maui Dive Shop.
Have a great time.
Liz