Codie's covered basically all the best areas on the SA coast.
If you really want a decent tigershark dive, check out this link, it's an awesome experience.
Diving with Tiger Sharks | Shark Adventures | Cape Town - tiger shark diving, tiger shark diving south africa.
For mantas and whale sharks I'd definitely head for the Inhambane area in Mocambique. I was up there in January and saw mantas on almost every dive on Manta Reef. Whale sharks are also plentiful in the area, saw 6 on one boat trip out to a dive site. We stayed at Guinjata Bay Resort which was really good (
Guinjata Bay Mozambique, guinjata bay offers year round diving on some the most spectacular reefs in the world guinjatabay has many varieties of rare and beautiful fish and sea life). However, most guys recommend Tofo Scuba (
::.. Tofo Scuba ..:: - Home). I've not dived with them yet but many swear by them.
In Southern Mocambique Ponta de Ouro/Ponta Molangane/Ponto Mamoli has some really good diving. All three resorts basically dive the same dive sites. There's good shark diving on Pinnacles Reef and night dives are often done. Mamoli is your upmarket resort, Ponta Molangane and Ponta de Oura are priced much the same but Ponta de Oura is much busier. It depends what you're after (after diving), a quite place or a bit of action. I usually go to Ponta de Ouro (on my daughter's request) and stay at Simply Scuba (
Simply Scuba Ponta Do Ouro - Southern Mozambique :: Welcome ::). I can't really compare them to other dive operators as they're the only operator I dive through when down there.
Enjoy your trip!!