I do not intend to sound like a snob here.....

I have been diving since 1981 and have seen a bunch of changes. Places that used to be wonderful such as Grand Cayman have become destroyed by the legions of novice divers that have pretty much destroyed half the decent dive sites off the island (Was there in 1984 and in 1998 and boy did it change). Sharm still has some great spots, however is dominated by "group" dive operators that take mostly Italians and French down, and they then proceed to get their bouyancy scrwed up and spend the whole dive destroying the reef and are more into the color coordination of their equipment than actually enjoying their diving. That said there are still some great spots in Sharm, but I would not go there in August due to the European crowds. I'd save it for a Jan/Feb when you'll appreciate the warm temperature more, and crowds will be more reasonable (If you wait until March/April its ok, but first check when Jellyfish egg season is as that 2 weeks is not the best to dive).

Bonaire or Turks are probably the best suggestions in the caribbean (cannot comment on Cuba). I personally find the Mediterranean and Aegean to be wastes of time (unless you have a specialized thing you like to do and can get licenses for like archeological stuff or spear fishing etc.).

I've heard some great thins about Kenya and Mozambique. Off the beat and track, some of the best diving I have had was near Dakak, which is in Northern Mindanao in the Phillipines (it is safe there). Truk and its surroundings are great as you have the whole wreck thing plus incredible sealife as well. If you go for the GBR, Heron Island is the place to go, much clearer than on shore and whitsunday diving and you are actually "on the reef" in a very ecologically friendly setting.