Hi,
I have been diving in many places arond the world and can tell you a few things:
1)The Pacific is much better than the Atlantic because basically it is a much older ocean which means it's creatures have had much longer to evolve.
2)The further west in the Pacific you go the more fish and other life you will see.
Living in Australia, I get to do a fair bit of diving on the Great Barrier Reef (my University even has a research station on One Tree Island). The Great Barrier Reef is very very good (much better than the Eastern Pacific, ie Hawaii, there is so many more fish and other creatures there) and Australia is also good because it is fairly cheap at the moment ($1 Aust. buys about 58 cents US.) and there are many different trips available. For example, I am going on a diving trip on the Outer Barrier Reef north of Carins, 5 days 4 nights liveaboard, for $250 US all inclusive except airfare to Cairns. This includes 14 day dives, 4 night dives, all equipment, meals, accomodation on the boat obviously, and so on. And Australia has the second highest diversity of fish anywhere in the world, after Fiji (although it may not be a good idea to go there at the moment). There must be at least 4 or 5 times as manyt fish and corals, both in numbers and types, as somewhere like Hawaii. Also, from Australia you can get out to places like Bouganville Reef in the Coral Sea, some of the most pristine reefs in the world. So that may be a good choice. However, for sheer diversity of life, you cannot go past soewhere like Palau, it has the most incredible diving in the whole world. The best people to go with seem to be ProDive, they are all over the world and seem to have some good deals from time to time.
Hope this Helps,
Tom
p.s. One place I've never been but would really like to go to one day is the Red Sea, that could be an amazing dive if you pick your spot carefully!