I just bought my D500 and Nauticam housing and so far, I love it. Coming from a D300 in a Sea & Sea MDX-D300, I looked at S & S first, because I had all the ports and gears. I preferred the control layout on the Nauticam, and then found out that:
1. The Nauticam comes with the optical trigger included.
2. Nauticam uses the same size port as Sea & Sea, and has adapters that are only $35 each and simply bolt on in about 10 minutes, replacing the bolt on back ring on the Sea & Sea ports. I bought 3, and they cover my standard port, my mini dome (even with a Sea & Sea to Nexus adapter on it) and my 20mm extension for when I use my big fisheye port.
3. I resisted the Nauticam vacuum system because I've never needed one before, but I'm finding it gives me great peace of mind for an extra $200+.
4. I far prefer the Nauticam camera base and housing closure system, and I love the port release and lens release system. I no longer have to take the whole housing apart in the boat to change a port or lens, just pop the port and pop the lens from the front.
5. Gear adapter for Nexus and Sea & Sea gears. For about $125, Nauticam has a two piece sandwiched adapter that goes over the Sea & Sea gear on any of your lenses, so you don't have to buy three or four more $2-300 gears. You can install it in 30 seconds.
6. I was worried about not having a top window, because I'm old and I have trouble reading the settings in the viewfinder sometimes, but Nauticam has a dedicated lever for the info button, so you can just hit it with your left thumb and have everything on big screen in giant black on white.
7. The review is also a left thumb lever, so you don't have to take your hand off to look at your last shot.
8. On my MDX-D300, I couldn't feel the shutter half press if I wanted to use it. (although I always use the AF-On button anyway). On the Nauticam, I can totally feel it and easily hold it at half press with my 5mil cold water gloves.
9. While Sea & Sea offers TTL, I have had terrible luck in the past with their external units failing in short order. While I'm sure the new internal ones are probably more reliable, I've heard great things about the Nauticam unit and will probably buy one. It's also easily owner installed.
Honestly, I don't think you can go wrong with either of the two housings, but there's my two cents.