More advanced operators on Maui are Ed Robinson's or Mike Severns in the Kihei area - if you're staying in south Maui ie. Kihei/Wailea. Advanced being relative although Ed's does offer a 3-tank Advanced Safari weekly. The Molokini Backwall is one advanced dive- often a live drop and drift. Down the wall you're likely to run into sharks - it's really vertical. Hard bottom is like 300'?
If you're staying in West Maui (Lahaina/Ka'anapali,Kapalua) I'd go out with Extended Horizons - the experience level may be mixed but they group/DM by level and choose multi-level sites - easy off Lana'i which they're likely to visit. Lahaina Divers also does their West Lanai Drift dives - I believe the minimum requirement is an Advanced Card or equivalent. I've been out there a couple times - fast drifts are pretty common. They also do a bluewater dive to Molokai looking for Hammerheads - probably the most advanced dive they do. It's better a certain time of year so ask them b4 booking. Their daily dives are going to be mixed-level groups often to Lana'i or the generic "Turtle Town" off the coast.
In West Maui the Carpathian used to be good for turtles - they sleep there also. One occasionally meets divers on descent. I think it's about 100' deep. I believe the only other boat option in Lahaina
now is Hawaiian Rafting - IDK them at all except they have a big RIB - we saw it once off Lanai.
There's really no difficult shore dives off Maui. Any that are more difficult will be related to getting down to them and not getting trashed while getting in over the lava. I really can't even think of one - most are sandy beach entries. Maybe check here:
Scuba Shore Diving Site Listing for: Maui Most of the Maui beaches are shallow for a long way out - we dove Old Airport once on scoters and maybe 15mins. out it was 60' deep.
You kind of want to pick an operator based on where you're staying. It's about a 45min. drive between the two areas and the Kihei boats all try to leave by 6AM so they're back b4 the tradewinds pick up. Smaller boats so often a smaller load. Severns might go with 12? max. My buddy did the 3-tank Advanced with Ed Robinson's a few years ago with about 6 total pax.
If you ever go back Sheraton Caverns off Kauai is the turtle spot - huge green turtles live there. And one of the more advanced dives in Hawaii is Keyhole or Vertical Awareness off Ni'ihau - an all day trip and a rough crossing. You might see a critically endangered Monk Seal there - otherwise
see them at the
Waikiki Aquarium, small facility but interesting 2nd oldest in the country. They have the coolest tanks outside - lava rock with glass sides - open air - sit and watch the reef fish. Also
Chambered Nautilus - the only place I've ever seen them.