The 4 places mentioned actually don't really do windsurfing..not at all in fact if I'm not wrong.
There are 2 main windsurfing clubs in singapore - Water Venture East Coast & Mana Mana. Both are located at east coast park and only about 30mins walk from each other.
Mana Mana has just started up, having been in Bintan previously. Water Venture has been around for years. Depending on whether you're thinking of learning windsurfing or are a seasoned sailor. Most of the windsurfers hang out at Water Venture these days.
You can check the local windsurfing scene at
www.bluefinz.com
If you want more details, just pm me.