Wow.
As a new member on this forum I am quite surprised by the conversation, particularly given that these destinations are in my country.
Anyway, for anyone who wants to know about SA diving, it truly is awesome. Sodwana is without doubt the diving mecca of SA, and as a result the main reefs are not as pristine as we would like. Compare 2-mile reef to a Guinjata Bay dive (in Mozambique) and you will see a difference. However, a relatively small proportion of divers make the trip to the further reefs, particularly 7-mile and 9-mile: these are absolutely world class! Even the smaller reefs such as stringer and ribbon are fabulous, and there are some other spots that only the better DM's know about... But I also have to confess that one of my best dives EVER was in fact on the southern portion of 2-mile reef (Antons, Caves, and finishing at Zambi Alley (where Bull Sharks used to be seen regularly)).
Thonga at Mabibi is definitely an awesome spot, as is Rocktail Bay further North. Yes, both very exclusive and very expensive, but if you can afford it the exclusivity is very nice and the diving is certainly some of the best. Can't argue with that.
For those of us who like to mingle in the dive community and enjoy the simple things in life, Sodwana takes the cake for this part of the coast. It does qualify as tropical as it is the furthest south that hard coral formations have formed in typical tropical profusion, and temps go as high as 29. The accommodation is varied, but we have always really enjoyed being self sufficient at the Parks Board Chalets (number 10 is the best!). Coral Divers is the biggest operator and have awesome facilities, but we have been lucky to get to know some of the DM's who take us on more unusual dives when it is not too busy. We don't stay with them, but they have good accommodation too. The after-dive facilities are awesome, and the evenings are a blast if you make friends. - a quiet sundowner by the pool often turns into a great conversation. Reefteach is also excellent for us eco-divers: very knowledgeable and guaranteed sightings of some of the rarer stuff.
However, I recommend you avoid the busy long weekends and holiday periods, especially Easter and Xmas: the beach gets completely overrun with the 4x4 crowd, and I like my peace and quiet.
Finally, and perhaps for a new thread, don't let anyone convince you that this is all - the entire coastline has great and varied diving, getting progressively colder as you approach the Cape but no less impressive in all the different ways the ocean has to offer. I am currently in Cape Town, and although a good 7mm with hoodie is required, the diving is amazing!
Hey - I should go into the marketing business!