Koh Samui has always been the step-sister of Phuket and Pattaya. It surely is more deserving as it offers the same or even more bang for the buck as compared to the other two destinations. The reason why KohSamui is more appealing is that it is a fair island and largely unspoiled. This is reason enough for you to want to head there. In addition, if you plan to spend 10-15 days at KohSamui and are a sucker for water sports, you will have something new to explore on each day of your trip. That is the kind of attraction this place holds.
While years back all you could see were jet skis which were a novelty then, now you find that quite a few jet skis have been purchased by private villas at KohSamui which are being used by their guests. So, while that has become a common feature, you can explore more adrenaline pumping water sports like parasailing, scuba diving, snorkeling and so on.
There are many privately owned water sports companies that offer tours and various packages that may be used but do ample research and digging around before you sign up. There are tons of websites that offer reviews of various water sports activities. These places offer courses if you are staying for an extended period. For instance, scuba diving can be undertaken as a course, a tour of real estate options on Samui can be found here. This will equip you to indulge in the sport no matter where you travel to.
Kite Boarding also offers something new if you have experienced most of the other options. Here the enthusiast will be harnessing the wind power with a power kite that can be controlled. They will be on a wakeboard or a surfboard with or without bindings. They typically use the wind to glide on the water.
So, no matter how serious you are about the water sports, there is an option for whatever you prefer!