Excited for you and your upcoming trip. If I can help you with any information or arrangements I'd love to do so. January is a great time for diving in Hawaii on any of the islands. Maui has AWESOME dives both off of the boat and shore. Your determinations may come from where you are staying. I agree with the suggestion for Ed Robinson's operation as an operator. My personal favorite is Mike Severns though you really can't go wrong with either. They are located south Maui and very close to the great diving at Molokini. In my opinion the shore dive at Makena Landing (also south) can often rival any boat diving as well when the conditions are right. The critters there (sharks, turtles, octopus, nudibranchs, etc... are amazing. Should you go with Mike Severns I would highly suggest setting up a dive with Pauline. She is simply amazing and one of the most respected, knowledgable and passionate divemasters in the Hawaiian islands. It's simply a CANT GO WRONG. To be fair ALL of her staff is incredible as well and I look up to them for their professionalism and overall operations. If you end up near to Lahaina I've had good experiences up there with Extended Horizons out of Mala Wharf. Mala Wharf is an incredible dive as well if you are interested in a CRAZY loaded critter dive. I "think" it can still be done from shore.
Kauai is entirely different underwater and you'll be lucky to see the variations in reef ecology in such a short distance between islands. All the diving will be done off the south shore at this time of year if that factors in to where you stay. There are several different operators that all run very good operations. The shore dive at Koloa Landing is amazing and a must do in my opinion. I've been diving here for over 12 years and I still dive the site on my days off. Currently there are Harlequin Shrimp, 4 adult and one baby frogfish, endemic lion fish, leaf and devil scorpions, freckled snake eels, turtles (of course) and many more great critters. It's a shallow dive maxing out at 45 ft which assures long bottom times. It's entrance is also fairly user friendly. It can be subject to lower vis at times but when it's fair to great - it's awesome. The whales are also coming back home this time of year so you can expect fantastic surface intervals watching these amazing Humpback Whales! It's also great to listen to vocalizations and song while you are underwater. Two of my personal favorites as dives from the boat are Sheraton Caverns (turtles/lava tube dive) and Turtle Bluffs (Whitetip reef sharks, moray eels, octopus, lobsters, nudibranchs and more).
I personally work for Fathom Five divers in Koloa/Poipu but think you'd find great passion and professionalism from any of the operators here.
Let me know if I can provide answers to any specific questions as you plans come together. I'm also very happy to but you in touch with any other company that may catch your eye and at least offer a suggestion on a divemaster to request.
Happy Holidays and best of wishes as you get ready for an awesome dive trip.
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