We went to the Big Island for a week and then Oahu for a week. I would go back to the big island ina heart beat, but now that we have done the Arizona have no desire to go back to Oahu -- traffic was terrible. 90% of the population of the state of Hawaii live on Oahu and then 90% of the population of Oahu lives in Honalulu. There is no road that goes all the way around the island so you have to go through downtown to get anywhere.
Snorkelling around the big island was amazing - lots of big fish, decent coral, lots of turtles! Snorkelled once off the beach in Oahu and could not figure out why theer was no fish. Later we saw several people going into the water with spears and bags!!
There is a flooded caldera that is a national park just outside of Honalulu that did have decent but lots of dead coral.
OOOOO! a UTOP with Hawaii!