The VCP hatch covers are the best. As long as the hatch rim is installed as they are on Valley Kayaks this hatch covers seal all the water out! 
The formula was changed a few years ago and now they hold up well to UV, but they don't float as the old Valley Hatches did. We still use 303 Protectant on them every few months to keep them soft and help them seal easier.We have been using these hatch covers for over two decades and still think they are worth the extra expense. Even without proper care the hatch covers will last many years. Proper treatment will extend the life to over ten years. VCP hatches are used on Necky Chathams, as day hatches on NDK and other kayaks, and of course on Valley Kayaks. While the VCP hatch covers are the best, how they are installed on the boat does make a big difference in water tightness. 
VCP recesses the cover so you get a triple seal. Most other companies makes the hatch cover rim flush with the deck, allowing only a double seal. This is still better than any other hatch covers we have used, but not 100% dry.
Kayak Sport (Kajak Sport) hatch covers are used on the bow and stern of NDK kayaks and on all three hatches of P&H and many other kayaks. They are almost water tight; in our experience they are not 100% dry. They hold up much better to UV and don't need to have 303 applied as often. The Kayak Sport hatch covers don't float, so tether them to the boat.
