OP
Thank you all for your comments!
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I prefer NIkon over the rest. I shoot Pentax usually, but have a Nikon for UW. Olympus is out for me, but the lenses IMHO for Nikon are better. I have a Tokina 12-24 f2.8 that I use for UW. Real fast lens and stopped down to F8 it is great.
I guess that I am confused. You say that lenses for Nikon are better but you are shooting the Tokina 12-24 f2.8. I don't think that there is in fact such a lens (I think it is f 4.) The Tokina 11-16 rectilinear is in fact f2.8. But if you are going to use Tokina lenses why do you think they work better for Nikon than the exact same lens does on a Canon?
Bill
I think that the mirrorless systems are quite neat and for the money not so bad on land but underwater the shutter/focus lag will drive you nuts.
Bill
I don't regard housing floods as inevitable. Use a little vigilance in o-ring lubrication and maintenance and it is not an issue, even under less-than-ideal conditions. I have gone about 15 years without one, dating back to a NikonosV and a Nikon F90x in a Subal housing, both of which had to be opened after every dive to change film. These days I can go a whole day without opening my housing, so flooding is even less likely.Finally, consider the apparent inevitability of not if, but when you flood your housing.