There are three types of drysuit on the market these days:
Compressed neoprene is reputed to be the toughest drysuit material around. It's also the most expensive. For the discussion below, assume compressed neoprene is a membrane.
Neoprene, the stuff used to make wetsuits, is also used to make drysuits (Which I found very confusing in my novice days when I thought neoprene was porous). Not too long ago, the vast majority of drysuits owned by recreational divers were neoprene.
More recently, membrane suits have become popular.
For an exhaustive discussion about the merits of the two types, check HERE.
My own thoughts on the matter are:
Drysuits provide you with two things: Insulation and bouyancy.
The more bouyant you are, the more lead you need. So, you don't want masses of bouyant insulation when it's fairly warm. You'll have to work harder, and you'll risk overheating.
A neoprene suit doesn't give you any options of reducing insulation, as the suit does the insulating. A membrane suit, however, has no intrinsic insulation. All the insulating is done my an undersuit, which can be changed as much as you like.
The deeper you go, the colder it gets. A membrane suit, because you add air to it as you descend, has a constant volume of air inside it. It therefore provides constant amounts of both bouyancy and insulation.
Neoprene, however, will be compressed by depth, robbing it of both bouyancy and insulation. The deeper you go, the colder and heavier you will become. In order to counter this, you must add air to either your BC, or your suit. The more air you put into the BC, the less streamlined you are. The more air gets put into the suit, the more bouyancy problems you leave yourself open to.
Neoprene suit wearers often say that if a drysuit floods, a neoprene suit is the best to be in, because the suit will protect you from the cold whereas a membrane suit leaves you with no insulation.
If you have a good waterproof undersuit, this argument holds no water. Ask anyone with a Weezle undersuit how much difference water in the suit makes to his warmth. The reply will be "None".
Also, you have to consider how often a suit really does flood. Neoprene seals are notoriously bad at keeping water out, and so neoprene wearers worry about floods. Latex seals on membrane suits either work fine or need replacing. A well-maintained membrane suit is not liable to flooding.
So, as an extreme example, consider a dive undertaken by two divers, one in neoprene, one in a membrane:
The deeper they go, the colder it gets, and the more they must rely on their suits for warmth.
The neoprene wearer looses insulation as the water temperature drops. The membrane wearer is just as warm as at the surface.
The divers arrive at the bottom, the neoprene wearer cold already. They establish neutral bouyancy by adding air to their BCs. The neoprene diver needs noticeably more air in his BC to become neutral.
The two swim along the ocean floor. The neoprene wearer is colder and working harder than his buddy. His breathing rate increases.
The dive ends, the divers start to ascend. The neoprene diver is more tired than his buddy, and has a harder time maintaining his bouyancy as he has more air to dump. He looses control of his bouyancy several times, ascending too fast until he gets back under control.
At the safety stop, the membrane wearer dumps air from his BC and puts it into his suit, increases it's insulating ability. The neoprene wearer has no such option.
Unfortunately, whilst on the stop, both divers rip their suits playing "Scissors, paper, stone" and the icy cold sea water rushes in. The neoprene diver has nothing between him and the water, and starts shivering. The membrane diver doesn't even notice the water as his undersuit is waterproof. They decide to end the safety stop early and surface.
Because he is cold, exhausted, has ascended fast, and not carried out a proper safety stop, the neoprene diver presents with symptoms of mild DCI. His warm, ready-for-another dive buddy who ascended at a safe speed is absolutely fine.
And that's why I went for a membrane suit.