I think part of the depends upon where you are going, and the likely hood of your bag getting lost/delayed. When I fly non-stop direct, I don't worry so much about luggage getting lost. If you are making transfers, than that is more of a possibility.
To date, I carry on my camera, and check my housing. But all the travel I have done has been using direct non-stop flights. I use a pelican case, and put it inside a soft bag.
I carry on a camera backpack with the majority of my camera equipment in that. However none of my diving camera equipment.
I check most of my dive gear. But I tend to carry on things that are heavy which is why I generally carry on lenses, and regs, and check things like my housing. And there in lies maybe a bigger question, how best to pack all your stuff, and stay under the 50lbs limit, and bag number limitation. Most flights now are charging $25 for the second bag, and some are charging that for each bag each way.
I find it difficult to travel with dive gear, camera gear, and UW photo gear. I can do it, but I use two 50lbs bags, and a heavy carry on to accomplish that. If I travel with my family (most of the time) we often have four bags between three of us, so not such an problem. When traveling alone, bringing all my equipment is not even possible, and I must leave some lenses behind.
Insure all your gear, and there is a bit less worry. However if my housing went missing, it would mean I would not be doing any UW photography. I seriously doubt most locations rent housings for a D200, but maybe a few!