I have been to the mentioned sites, but have to add the Gulf of Thailand for completition. Nowhere else i have seen that many Whale Sharks as on Sail Rock (situated in between Koh Phangan and Koh Tao). Best time to see them is around March-April and Sebtember to November. Last winter-season we've had multiple sightings daily! Sometimes up to 5 specimen at a time.

Anyway, Thailand is top notch for a dive holiday! I won't get boring. Neither beneath nor above the surface.