I have used both the Sea and Sea housing and the Ikelite housings for the D200.
Here's what I thought...
The S&S is more durable, made from aluminum (I believe) - it's labeled on the outside of the housing... and all of the controls are precise and easy to use. The shutter action is also cooler than the ike. as a side note, the front action wheel on my ikelite housing (the F-Stop adjustment when in Manual mode) has given me problems, and I've had a total of 4 dives where the camera was "stuck" in the F-Stop that I was in... in one case it was F8 which wasn't SO bad - but anyway, it should function perfectly, which the S&S did.
Also - the next main difference is the ports -
1) The Ike ports are acrylic, and can scratch fairly easily... the S&S ports are glass
2) the ike ports clip in with 2 "retaining clips" - the S&S you push and turn on similar to a lens.
3) the way the zoom lenses interact with both are different too... Ike has an acrylic zoom gear which is somewhat generic... the S&S has a zoom gear for each specific lens.
The last big thing is the TTL. Basically, Ike has it - and nobody else does (have it built in).
In other words... the ikelite has the iTTL control on the back of the housing... it's really easy to use. S&S if you want to use TTL, you have to purchase an additional TTL converter (MORE MONEY)
So - my choice for now is the Ikelite... If I come up with a spare $3000+ I may sell my ike and get a S&S, but for now, I'll use the ike... The pictures come out the same.
You can get an Ike with a port for about $1500
You can get a S&S with port and TTL converter for about $3700
That's my 2¢