As written by an idiot, so please feel free, all, to correct as required!
Membrane Suits
As said, made of a thin material, including trilaminate, or the slightly fuzzy cordura. They have no insulation properties, so you will need a good range of undergarments. An thickish undersuit, plus thermals/base layers, for when its really cold. Resonably flexible, easy to dry (mine is anyway), pretty hard wareing. Can look baggy and unftted, if not, well..... fitted!
Neoprene
Thick air bubble filled material, about 6mm (I think). Much warmer than a membrane, so less undergarments required. The neoprene will compress at depth though, so will loose insulation. More flexible than membrane, and a bit stretchy. Usually a closer fit, as less is worn under it. Warmer if it floods. Not as hard wareing (think of all the nicks you can easily pick up in neoprene wet suits!)
Compressed neoprene.
As above, but the material is compressed and injected with a resin (or something), to keep it compressed. Less insulation than neoprene, nut more than membrane. Will not compress with depth. Very hard wareing, but not as flexible as neoprene. These will cost you plenty though!
Personally I have an otter membrane (though still not used it outdoors yet
.) The choise is purely personal, as each has its benifits, and drawbacks. Just make sure it fits well, you can reach your valves and are still flexible, and you can get enough on under it to stay warm. I would recommend you get a suit with thigh pockets, or at least get them fitted aftermarket!
Hope this helps
Rookie (self confessed idiot)
Please note, the above content may be full of crap!