I have owned and dove two trilams and have dove and owned two neoprene suits.
I prefer and dive a neoprene suit. In extremely cold water the neoprene suit is warmer and it can be dove with much less bulky underwear while still keeping you warm. I should add here that I also dive reasonably deep to 150 ft dephts with 35-39 degree F bottom temps, so they are still warm at depth despite years of DUI propoganda that contends otherwise.
Neoprene suits also swim very much like a wet suit with virtually none of the bulkiness and wrinkles that accompany trilam dry suits. The inherent stretch of the fabric allows much more flexibility with a very trim and close fitting cut to the suit. Trilams have to be long in the torso and loose generally everywhere to allow full range of motion with the non stretching fabric. So in my experience a neoprene suit is much lower drag than a trilam and leaves you with at least as much or flexibility. Plus in my experience, you can go head down/feet up ina neoprene suit with no concern for losing control and no need to resort to a tuck and roll to recover to a normal swimming position.
This is due in part to the closer fit of a neoprene suit but also to the ability for the diver to dive with much less air a neoprene suit as the squeeze that accompanies an under inflated neoprene suit is not the painful pinching variety that you get in a trilam suit.
It's true you can quickly over heat in a neoprene suit in hot weather so careful planning with all gear prep being done prior to suiting up is important. However, a quick dip to get the suit wet results in it functioning like a large swamp cooler and the heat absorbed by the evaporating water cools the suit and keeps you reasonably comfortable. In cold weather this can work against you however, so after a winter ice dive, expecially in windy weather, I will immediately don a wind proof rain suit over the neoprene dry suit to minimize evaporatative cooling and keep warm during the surface interval.
A trilam probably lasts 2-3 time longer than a neoprene suit, but it also costs 3-4 times as much to start with so it's a question of owning one trilam until it dies or going with 2 or 3 neoprene suits (each with new zippers, valves, boots, and seals) that consequently do not cost money to replace as they would on a trilam. In the end, the 2 or 3 neoprene suits are still cheaper in the long run.
Neoprene seals are also much warmer and much more durable. It's rare to ever have to change them out on a neoprene suit. However if you do get a leak in the fabric itself, it's a bit harder to find and fix than on a trilam.
Weight wise, I dive virtually the same weight with either a trilam or neoprene drysuit. Older neoprene suits with chest mounted exhaust valves did require lots of additional weight due to greater trapped air space, but there is not any difference between with modern neoprene suits and trilams with regard to weight requirements.
