Hi guys/gals thought I would bump this thread and give my opinion, I am a scuba diver and worked in the industry. While not kayaking dry-suits the principle is the same and I have also learn't a little from using my own surface dry-suit (F4 Northern Diver) on my AI.
Latex seals generally come in two grades, "heavy duty" and "standard", the heavy duty seals are similar in comfort (slightly better) to neoprene seals, stiff, poor seal and uncomfortable, compared to the "standard seals" a lot more soft / comfortable when trimmed properly. The problem with latex is they are a lot more susceptible to UV and will degrade rapidly if not cared for. If you can get a suit that has a thin overlapping two piece neoprene collar to protect your latex seal and not choke you, you will be way better off.
Latex seals will also give a better seal, especially on the surface where there is no water pressure to help make the seal and is the best choice for people who have very thin sinewy/bone'y wrists and ankles. Some people are allergic to latex and previously had no choice but to get neoprene seals and then find they will not seal due to thin sinewy/bone'y wrists and ankles. Then "bio-seals" were made, they are a very thin flexible material with no latex and not only do they make a better seal they are also more comfortable and in recent years have also been found to be beneficial to comfort for latex users as well.
You can buy products to soften/lubricate your latex seals and I highly recommend doing it to keep them supple and protected to increase longevity of life.
I would also recommend latex wrist seals that are covered with a cuff and ankle seals (the same with cuff) or fitted socks. Now with fitted socks some manufacturers have an option between latex and neoprene. Latex socks you will need to wear boots and you will need to make sure between the boots and leg cuffs (if your suit has them) that your latex socks are covered as they are probably more expensive to replace and are more susceptible to UV light and continious stress. I like Neoprene socks, I find them less susceptible to UV, easier to put on, more comfortable to touch/wear and they have the option to either wear them on there own or you can add boots for more warmth and better protection from rocks etc if they are present.
As with my suit the zip is across the shoulders on the back and while I was flexible, could manage to zip/unzip but now cannot due to neck fusion, I would not recommend a rear entry suit unless you "always" have someone with you.
The other style of entry zip is front and there are two different styles here, one is a diagonal zip across the front from the top of your shoulder to the opposite waist and the other is in a large flap that wraps around your your chest. Almost all the manufacturers use the diagonal zip which I have heard can rub on the shoulder when paddling causing a lot of discomfort and chafe and can puck up due to the stiffness of the zip but apart from that can be easy to don/dof on your own and easy to use with no crimping/bending to the zip, good for pedal kayaks.
The second is only available that I know of in a suit made by Northern Diver (UK) called the "Aquarius", this suit is designed for the military, police and rescue services. It has an extra long cut to allow freedom of (running) movement (extra leg length) ideal for pedal kayaks, and an extra long torso cut for don/dof of the suit which in my opinion also helps stop ridding in the crotch when seated. The best thing though is the large entry and how the zip wraps around your chest, no bunching up and no shoulder chafe. Down side is it is only available in black unless a "huge" special order is made, it also comes fitted with big ugly gumboots that will most definitely chafe around the legs (they can be changed at buyers expense) and they are a diving suit so if you do not want all the extra valves fitted you must special order no fittings, stupid part is; they still come with the suit, you still pay for them, they are just not fitted and the holes are not cut. Ow the other downside, darn expensive.
I have only tried one of these on, not used it, so I have no idea of it's breathing qualities, wish I could afford one to find out.
Zips, the most expensive part of a dry-suit is the zip and make sure the zip is a YKK heavy duty, the plastic ziplock (plastic lunch bag style) dry zips are more susceptible to damage from sand grit etc and will also brake open easier than a YKK when under stress.
"DO NOT BEND YOUR ZIP"
"KEEP YOUR ZIP WELL LUBRICATED".
Most zips also have latex in them and yes you guessed it, susceptible to UV, try to get a suit that has a zip flap to protect it from sunlight. Also get a good carry bag that protects it from light, bending of the zip and dirt/grime that may damage zips and seals, even better if it opens right up and doubles as a ground sheet to don/dof your suit on rather than the dirt or sand.
Toilet issues, GET A RELIEF ZIP or PEE VALVE. The first option is more practicable for men unless the suit also doubles for scuba diving, the second option is best for women as they can incorporate it with a "ShePee" and not have to worry about shedding the suit, men use a catheter condom. If you go down the "Pee Valve" road you will have to buy the accessories needed on a continuous basis, you will also find you will have to sit side saddle or even get into the water for it to properly work.
Very few surface dry-suits have very much thermal quality, it is all about layering or the lack of, but even on a warm day you will find a thin layer of clothes is needed to "stay warm", remember, "YOU ARE DRESSING FOR IMMERSION" not comfort!!
Breathable suits are also very desirable as is an undergarment that wicks sweat, you are best to get any sweat away from your skin to help stay warm, breathable suits will help control the sweat.
Another safety issue is if you go head first into the water without a PFD (which wont happen if you are responsible and always wear a PFD) is that the air will go to your feet and keep you "bum up", it is a good idea if you buy a dry-suit to train yourself (in a controlled environment - with a buddy) how to tuck and somersault. If you can tuck and somersault you will transfer the air from your ankles to your chest which will then act as a form of life vest. Try not to wear external belts, belts will restrict air flow through the suit. Get a suit with internal braces so they hold the suit up, I also cross the braces over to the opposite sides as it stops them from riding down over the shoulder and annoying the crap out of me .
When you get in a dry-suit, do not vent all the air out, keep as much as you can comfortably keep. The air is your thermal protective layer that keeps the cold water surface area away from your bodies core heat and will keep you warmer in an immersion situation.
Good luck and safe comfortable dry-suiting.