The W10 is a very nice camera with plenty of great features. The image quality is excellent and it even does a pretty good job with video (I think that most of the video clips that Holy Mackerel has posted were shot with his W10). I've been using mine for a couple of months now and I'm very happy with it. I just saw a W20 on display and had to fight back the urge to buy. If you are going to be using the W10 or W20 on the water you should get the silicone skin. The W10 is very smooth and does not provide much of a gripping surface. The silicone skin should make it easier to hang on to. I just put a layer of Goop silicone adhesive on mine. It works, but looks ugly. Other than the grip, the only problem I have with it is the lack of a lens cap. I keep my camera in the pocket of my PFD, so it is always close at hand when I need to take a picture. If you have any water on the lens the pictures will come out with some very interesting distortions. Worse yet; if salt water dries you will have salt crystals stuck to the lens. I try to keep some fresh water on hand to rinse off the camera if needed. Now I keep the camera in a zip-lock bag inside my PFD pocket. The leash on the camera keeps the bag from sealing, but it still does a good job of protecting the camera from splashes.
I'd go with the Pentax. For my money, there isn't a better waterproof camera on the market.