Depends I shoot with a d800 in a subal housing. If I was starting out fresh I would have a nautical hosuing as the parts are easier to get now than Subals. I have had 4 subal housings so I kept the ports thru most of them until Subal changed to larger ports I went with them back then. Now Subal is experiencing prodution issues and financial issues so parts are a bear to get.
I know a pro who is shooting the D850 as he wanted the newer features of that camera and he will stay with that camera most likely until he done shooting he said.
I am very pleased with my Subal and D800-I personally do not like the plastic housing Ikelite makes-in the old days they flexed and controls bound uop at depth (Truk lagoon deco dives) I would stick to better housings-Sea and Sea are short on full controls-wear as Subal and especially Nauticam gives you all the contol functions .Nauticams are especially well thought out and maybe a bit over engineered-they are easy to get parts and service-not so much with Subals anymore.Seacams are also under contolled in my view-(not all funtions work)
In housings you get what you pay for.Whatever housing you start with after buying all the ports (glass ones are best) you tend to keep the ports and change the camera and housing body as time goes buy.
The D800 is a super camera no question-maybe a D850 if starting new? of course you will need two bodies right?