I've been happily shooting a D200 in an Aquatica housing for the past couple of years. To me, the housing afforded the best value in terms of what I was looking for. I had owned an Ikelite housing for my D70 prior to moving to the D200, and decided to go with the Aquatica for a variety of reasons. I would emphasize that the Ikelite housing is a fine housing, but there were a few things that I found to be better with the Aquatica.
I mentioned this already in another thread, but the gearing on the Aquatica I found to be more precise. I was having some issues on the Ikelite housing (especially when under pressure at depth) and eventually ended up stripping some of the gears over time. I also found I like the tactile feel on the levers of the Aquatica better. Not so much a big deal in warm water when not wearing gloves, but it seems to make a difference to me in cold water while wearing thick drygloves.
The other factor was having multiple ports for macro (and the 6" domes) for different lenses rather than port extensions. This means buying a port for each lens - with the exception of the 8" dome system.
The other thing that I really liked about the Aquatica was the rail mounting system for the camera body. There's very little play in the positioning of the camera body. With the Ikelite, mounting system, it did move a little bit and I found the command dial levers did not always contact the camera body optimally and there was a fair bit of slippage, which does not happen with the Aquatica.
The disadvantage of the Aquatica is that there is no TTL, although I think you can buy an optional TTL module for it. I'm not a huge user of TTL, so that didn't really matter much to me in the end.
Also being a Canadian company, this was an advantage since I got Canadian dollar pricing (at the time the C$ was much lower than the US$) so that was an advantage to me.
These are just my own personal experiences and observations, having owned and used both housing systems extensively, and of course, YMMV.