Roratonga, Cook Islands

[Delphinus]

I would imagine the comparison to be a bit of an apples-vs-oranges thing ... although both are tropical islands Would think Maui is a lot cheaper, although I guess with the $USD thing maybe not so. It's definitely faster (usually direct flights available). Roratonga is further south so the reef diversity will be greater. Best description I ever heard that describes Pacific reefs is this: Papua New Guinea is "ground zero" with the largest biodiversity. As you get further away from ground zero that diversity falls off. Hawaii has nice reefs but is quite a way's north and the waters are cooler in comparison. As a result, only hardier corals such as Pocillipora's and smaller - no tridacnid clams, no anemones. Fantastic fish load though.

I doubt you'd regret either choice but I think that if Roratonga is seriously on the map of possibilities I'd just say go for it and go there. If it isn't possible for some reason then consider Hawaii. It's not like you'll hate it there.