Koh Tao is beautiful and home to a number of dive schools close to some of the best diving spots you'll find anywhere in Thailand or Southeast Asia. It's also relatively cheap to get certified here, especially compared with other parts of the world, which is why so many flock here to learn to navigate undersea depths. Though it's certainly no off-the-beaten-path destination, Koh Tao is less tourist-laden than both Samui and Phangan.