Don, you'll probably come up with as many opinions as there are manufacturers. Basically, you have to decide what features you want in your drysuit & how much you want to pay for those features. DO YOUR HOMEWORK, THEN DECIDE.
As you probably already know, drysuits provide the most exposure protection by keeping water away from your skin. Their warmth lies in several things: (1) the basic thermal properties of the drysuit material itself; (2) the type & amount of garments you wear under the suit. (3) how much air you put into the suit.
Wearing a drysuit is akin to wearing a big pair of sleepers: you are encased from neck to toe in the suit, with your head & hands exposed. Most suits are back entry, which means that someone has to zip you in & out of the suit. The two self donning makes that come to mind right now are DUI and Abyss. There may well be more out there...
SUIT MATERIALS
Basically, suits fall into 2 categories: shell or neoprene. Shells can be anything from vulcanized rubber to tri-laminates (3 layers of various materials, one of which is usually nylon). Neoprenes can be the usual 1/4" closed cell or the more exotic crushed neoprene. Fit is important in either suit: you should have a full range of motion regardless of what the suit is made from.
Shells give some protection against the temperature of the outside water; however, what you wear underneath them is the determining factor in how warm you will be. You can wear anything from a t-shirt & shorts to full "woolly bears", or multiple layers of clothing. Shell materials have minimal buoyancy characteristics, so you require less weight to be neutrally buoyant.
Regular 1/4' neoprene gives you a lot of insulation against the cold (outside water), but it also means more inherent buoyancy. Thus, you must wear more weight to be neutrally buoyant. Again, what you wear depends entirely on how warm you want to be. Like it's wetsuit cousin, 1/4" tends to be somewhat restrictive unless fitted properly. They are usually the most economically priced suits.
Crushed neoprene is only available through a couple of manufacturers. Because all the N2 bubbles in the neoprene have been "crushed" out of it, it has very little buoyancy of its own. It is heavier, more durable, flexible, and gives more insulation than tri-lams. However, since it is a patented product only available through a couple of manufacturers (like DUI) it is very expensive.
SEALS
Drysuits seal at the neck & wrists. Seals are made of two materials: latex or neoprene.
Latex is suppler, conforms well to the contours of the body, is less restrictive and so easier to adapt to & fit. However, it is also more expensive than neoprene, tears easily, is higher maintenance, and has no thermal properties (colder).
Neoprene is less expensive, very forgiving of abuse, requires less maintenance, and has some thermal properties of it's own (warmer). However, it is less supple than latex (more restrictive), and thus may takes a little longer to "get used to".
ZIPPER
Arguably, this is the most important and most expensive part of the drysuit. If this item "goes" it is literally HUNDREDS of dollars to replace, because of its highly specialized nature. There are particular care requirements to this type of zipper, but they are minimal and easy to incorporate into your usual routine of good equipment maintenance. Like most dive gear, if you take good care of your drysuit, it will take good care of you.
MISC
Generally, drysuit divers tend to need about the same amount of weight as someone diving wet in 1/4" neoprene, EXCEPT if you opt for 1/4" neoprene drysuit... air+ neoprene = more weight. Also, drysuit divers tend to need/use ankle weights, although this is not always the case.
You have made a wise decision to take a drysuit course. A drysuit is not just a passive piece of equipment that you can put on & use. Divers new to drysuit diving need to learn the proper & SAFE way to use the suit.
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My first drysuit was a 1/4" neoprene back entry Wardell with neoprene seals. At $600 Cdn it was a great intro suit, even though as an "older model" it had a few quirks like a manual exhaust valve located on the left side of the chest. The coldest water temp I dove in it was about 35F.
Now, several years later here in the US I'm using a DUI self-donning trilam (350TLS) with neoprene seals & Rock Boots. So far the coldest water I've been in with it has been approx. 58F. It cost considerably more that $600Cdn!
BTW, you can get some great prices on used suits from dive stores, or from manufactures/stores where someone has put a deposit on a custom suit then left it. But as in anything, caveat emptor... let the buyer beware!
All that being said, no one who dives dry ever goes back to diving wet, except in tropical waters. Its just makes diving temperate waters so much better. So says someone from The Great White North, eh? (aka Canada.)!
Good luck,
~SubMariner~
