I recently (last May) switched to a Fusion and in the 15 or so years before that dove various trilam suits, a couple neoprene suits and demoed crushed neoprene and vulcanized rubber suits.
I like the fusion in terms of swimability and range of motion. The combination of a fairly generously cut inner bladder and a stretchy outer skin lets you use a suit that is cut baggy but does not have the drag and air management issues that would otherwise accompany a baggy dry suit. The benefit is that a few sizes fit everyone well and the suit is very tolerant of weight or undergarment changes.
The downside of the Fusion is that it is indeed a PITA to get in an out of compared to a trilam or even a neoprene dry suit. It gets better with time and practice, but if you let the inner layer get too far ahead of the outer layer when putting it on, life gets intertesting.
A trilam is easy to get into but since the material has no stretch, it also has to be cut fairly baggy to allow a full range of motion. With no outer skin, this means lots of wrinkles, more drag more volume for air to migrate to during the dive. So the fit and cut of the suit becomes much more critical. Too snug and you will have limited mobility, too large and the suit will be excessively wrinkly, draggy and hard to manage. It is a fine line and a trilam suit is not real accommodating to weight or undergarment changes. You can get a trilam with a self entry zipper but the cross chest self zipper requires a longer torso than the non self entry across the shoulder zipper and that extra lenght has to be managed. In the case of DUI self entry trilams they go over board with it and then add a crotch strap to control the folded torso.
Andy's used to make excellent trilam dry suits and used a curving shoulder to shoulder front mounted zipper (just like the Fusion - I suspect Whites bought the patent on it). It made self entry very easy with no need for extra torso lenght.
Neoprene suits (the uncompressed variety) acquired a bad reputation back when they were about the only game in town and when they had chest mounted exhaust valves and fairly baggy cuts. They needed large mounts of lead to get down. However the current crop of neoprene dry suits are cut very trim, relying on the natural stretch of the material to provide flexibility. Consequently a 7mm or 7mm/5mm neoprene dry suit will not require significantly more weight than a 7mm full wet suit and will swim much like a wet suit in the water but will be much warmer even with only light weight undergarments. They are however heavy, dry slow and leaks can be very hard to find. They only last about 1/3 to 1/2 as long as a trilam but then they also only cost about 1/3 as much as a trilam. The zipper option is also across the shoulders only. One les known benefit of the neoprene suit is that it is less prone to squeeze and squeezes do not have the sharp biting quality associated with a trilam. The Fusion is very similar to a neoprene suit in this regard.
Compressed neoprene is a bit of a compromise. It has some stretch and can be cut a bit snugger than a trilam, has some inherent insulation and does not sqeeze quite as bad as a trilam. But it is not as flexible as a neoprene suit and has the same heavy, slow drying and hard to find leaks qualities. But they are well known for durability.
Vulcanized rubber suits are incredibly tough, but have to be cut large as there is very little stretch to the material and are consequently baggy and draggy. Rear entry acreross the shoulders zippers are about the only option. They are very heavy heavy but dry very fast, are very easy to repair (5 minutes with a tire patch kit) and are the only suit you realy want in a contaminated water environment as they are easy to rinse and very chemical resistant.
On balance I prefer the Fusion over any other dry suit I have ever owned or currently own. It fills the same category of a due everything general purpose wreck/tech/rec dry suit as a trilam does, but has much more swimmability, comfort and flexibility in the water. You just have to put up with the slightly more bother some process of donning of the suit.
If I were just ice diving in the artic, I'd use a neoprene suit, and if I only dove in nuclear reactors or leech pits, I'd dive a vulcanized rubber suit.
