I dove the Seychelles. Due to El Nino the water temperature rose and bleached the coral. It now looks like the seabed has been dynamited. The fish are still around though: great variety, colours and also snorkelled above a whale shark! Turtles and dolphins too! On Mahe I recommend Dive Seychelles at the Mahe Beach Hotel. Run by 2 S Africans with a Scandinavian DM as well as local DM and Boat skipper. It is the most professional outfit on the island.

The real bonus is that the Seychelles are a dream destination, beautiful uncrowded idyllic beaches, a friendly local population, excellent weather just the most beautiful place in the world for 2-3 weeks.

I'll chime in and vote for Grand Cayman and Bonaire. Usually more $$$ than cozumel, but a great experience!

Tough call, there are so many great places to go, combined with local flair - wow!! where to begin. Generally most divers would agree on Cayman, Bonaire and Honduras for top 3 in the Carribean.
For the rest of the world South Pacific and Barrier reef are all Goood!!