Underwater housing - quality of ports

I am considering various housing for my D70. One of the consideration is the quality of the port. Could anyone tell me whether there is any significant difference in term of the front lens quality of ports from different makers, such as Ikelite, Aquatica, Nexus etc.

Thanks.

I think glass vs acrylic debate for port is not such a big deal. Afterall, you get lots of water in between the subject and the lens that will degrade the picture much more so than glass or acrylic.
Personally I think they are all fine but each manufacturers have their own quirks that you may or may not like.
Nexus by far as the most interesting port system as they make small domes specifically for each wide angle lens so your system is much more compact than other brands. Its macro port is tapered so it also look somewhat smaller and more compact as well. Pretty nice design for the ports really. Ikelite has the advantage of cheaper ports but each lens requires its own port so you will have more gears to carry. Subal, Seacam, Sea and Sea all have big dome and macro ports that you can add extension rings for various lenses so you have less stuffs to carry but more o-ring to deal with. Not all housing manufacturers support all the lenses so I would figure what lens I want then see what combinations of ports/rings etc I would need and see which brand make the most senses. Ikelite and Sea and Sea do not seem to support the high end camera like 1Ds MkII or D2X so if you want to upgrade eventually, you may end up having to buy all the new ports as well if you go with those brands.

Ikelite:
By far the least expensive, but if you build an extensive lens kit there is going to be some bulk for travel. Ikelite does not offer extension rings, so if you wanted to shoot 10.5, 12-24, and 18-70, you are carrying around 3 domes, and if you want to shoot a 60 & a 105, you are adding 2 flat ports into the mix... Glass fronts for macro ports, 6" diameter plexi- domes for wide angles, 8" port in the works for Nikon 12-24 & Canon 10-22. Ikelite has limited support for super macro setups.

Aquatica-
1 8" dome, plastic, placed by varying port extensions. Nice wide mount, so nearly any lens will fit. Macro port front is acrylic, which is a really poor material for a macro port (scratches easily, likely noticably more chromatic aberration). Good gear support for most lenses.

Nexus-
Many glass domes to choose from that engineered for specific lenses, as well as "generic" 170mm & 230mm acrylic domes. Athena, a third party manufacturer, also supports these housings w/ a 170mm glasss dome that is very highly regarded. There are basic flat ports (autofocus only), as well as flat ports with focus (af & mf with the 60 & 105 lenses), and the multiport which supports the 60, 105, 70-180, and 200mm Nikon Macros. The multiport is the ONLY setup that allows MF, Zoom, and Auto to Manual switching with the exotic Nikon 70-180 macro. My suggestion for people starting out with Nexus is the multiport, and an Athena glass dome for maximum versatility.

We also sell Subal, which has a very nice glass fisheye dome, excellent macro ports, and very well designed lens gears that are easy to mount and line up easily. Subal ports are actually milled from delrin to keep their weight down and retain near-neutral underwater handling for the housing.