Hi guys! I have some opinion about Koh Samui diving. Instead of going to Koh Samui for diving i'd recommend going to another island called Koh Tao. Since most of the dive sites are around Koh Tao, like Chumphon Pinnacle, Sail Rock, Nang Yuan Pinnacle are all easy access from Koh Tao (i mean shorter boat ride). Koh Tao is not as big as Koh Samui, which is 3 times bigger than Koh Tao.But they have the best diving facilities as most people go there to DIVE!
Ban's Diving Village, Scuba Junction, Big Blue, Seashell just to name a few. There's a lot more!!
Like in Koh Samui, it's big, it's more expensive (compare to Tao) and you can see almost every white men on the island have local 'chicks'..unless your objective apart from diving is to get laid..then it's different story.