Beyond it being waterproof, what are you looking for?
: $400, 12Mp, no zoom, 90*-170* wide angle lens, don't know how deep you can go with it, my guess is snorkeling deep. Will shoot high speed video so playback can be in slow motion at 720 & 1080 HD quality.
PENTAX - WG-3
: $250, 16mp, 4x optical zoom, wide range of shooting presets, 45ft depth
. optional GPS
tagging for and extra $20-40. Will shoot HiDynamicRange, 1080HD movies. Will shoot time lapse and save as an MPEG movie
: $500, 5x optical zoom, 14Mp, 200ft depth
, f/2.8, 720 HD movies.
If you want to take action videos with the camera attached to your person or to some part of a boat, then go with the GoPro. I don't know how good they are for still shots, I think they have been optimized for action videos. My guess is pretty tolerant of being banged and dropped.
If you want to SCUBA with a camera then a SeaLife is the way to go. They have other models.
If you want a point and shoot that can come on deck
during a storm or go ashore in a dinghy
thru surf or to go snorkeling with then the Pentax is the way to go. Based on personal experience with an earlier model Pentax it has taken a lot of abuse and still works acceptably. Newer models are even more shock resistant. Will do high speed movies at VGA quality.
Pentax and Olympus were the early developers of Waterproof digitals and seem to have the most features currently. The high end Olympus to compare to the Pentax is the Olympus Tough TG-830 iHS
Pentax has the advantage over Olympus with an f/2.0 aperature vs f/3.9, so it will do significantly better in low light. The Olympus has the advantage of a 5x optical zoom with some fancy something that will get you 10x zoom without it being a digital zoom. The Olympus is good to 33ft instead of 45 but if you are trying to go past 33' you should be in a scuba rig and have the SeaLife.
Over all I would go with a Pentax unless you have a specific need that can only be filled by a SeaLife or the GoPro.