For Maui:
I tried most of the operators out of Kehei and by far my favorite is Ed Robinsons' for many reasons, but I prefer more advanced diving and as a photographer my interests may be different than yours. Be sure you tell them what you want. Ed's is real good about grouping divers of similar skill and desire. Mike Severns is my back up. Suggestion; I recommend that you book your dives before you go, I learned the hard way. Many of the good operators are full and you would not want to miss precious days not diving.
Lahania divers has impressed many folks, I am not amoung them, and am hoping I just had a couple of off days with them. I made the 45min drive each morning to Eds after a couple of bad days.
Don't forget to check out the aquarium to see examples of what you should be seeing while diving. Also there is a nice Italian restaurant near the Kehei police station.
Oahu:
I was impressed with Ocean concepts, though their dives sites seemed limited.
Aarons: I was extremely dissappointed with, they charged for dives they cancelled and it took several days and many phone calls to get it cleaned up. I prefer the folks who have a business that is successful enough that they don't charge until you either get on the boat or finish your dives. Charging a week ahead makes me think they are not doing well, and that of course makes you wonder why.
Have a great trip!