I was interested in an underwater housing too and asked @getolympus if it was on the product roadmap, he said: Not that I'm aware of at this time. How's that for vague?
The Canon wins then the Pentax. The rest are pure crap, especially the Olympus Tough 8000. This is about the 5th generation Oly, yet it hasn't improved one bit.
I'm thinking of getting something like a Canon G10 and housing. A lot dearer, but vastly superior.
Equinox HD6 Underwater Video Housing Kit with Canon VIXIA HF S10 HD Camcorder at B&H or Adorama. Very high end though but the results are "pro publish quality both stills and video.
I know you are looking for a housing but B&H has just housings also.
Dan