All the islands have similar macro opportunities in my humble opinion. Wildlife does vary for sure in the 500 mile stretch between Kauai and Big Isle with many consistent small critters for sure. I encourage photographers to really consider shore diving options for personalized dives with a small or even private group. Shore dives with the right guide/company typically yield amazing results and a slow - critter intensive pace. Many of the dives also offer easy entry/exit. As you narrow your island choice, I'd be happy to put you in touch with guides/companies that I have personally used. I can also suggest sites that are great for small critters.
Kauai has an awesome shore dive called Koloa Landing that is LOADED with macro opportunities. I dive there numerous times a month just for photography. Some of the current macro highlights include...
Harlequin Shrimp
Leaf Scorpion Fish
Endemic Freckled Snake Eels
Dragon Morays
Blue Dragon Nudibranchs
White Margin Nudibranchs
Commerson Frogfish
(These are daily highlights currently)
You'll also see lots of turtles, various moray species, countless inverts, devil scorpion fish ...etc....
As it is home, I certainly know more about Kauai than the other islands current hot spots.
I don't think you are going to go wrong with any of the islands for your macro/photo needs. The trick is in finding a guide/company that is happy to cater to your photography needs which can be done easily be done with a little research. It's a crazy time here on the islands for guides and I think that's why you haven't gotten more replies just yet - but I am sure they will filter in.
Feel free to personal message me with any specific questions you have. I'd be more than happy to try to help you out as best I can.
Best of ocean wishes and Happy New Year to you!
A