I agree with the comment on sitech valves, they are a big selling point no matter who makes the suit and given a choice between two suits that were otherwise comparable, I'd go with the one with sitech valves every time.
I own a Diamond Trilam drysuit and I am impressed with the weight of the fabric (heavier than a TLS 350), the zipper (one of the largest and most durable I have seen on a dry suit), and the sitech valves. I also own a Scubapro Cape Horn. I am not sure who made it for SP, but with the exception of a crappy exhaust valve it is a good suit.
Viking and Nokia both make excellent vulcanized rubber suits and vulcanized rubber suits are a good choice if you are diving in environments where the suit is exposed to a lot of potential hazards. In a 1200 or 1600 weight they are very durable and regardless of weight, they are very quick and easy to repair. They also have some stretch to them, unlike a tri-lam and a little more steamlined fit is possible.
Neoprene suits were looked down upon for years after trilams hit the market, but they also make a good option and seem to be making a general comeback. They have a good deal of inherent warmth, even if punctured, and are normally warmer than a shell suit with less bulk when all is said and done making them a good choice for really cold water. They are also quite stretchy so a snugger and more streamlined fit can be maintained. My spouse has used an Atlan 7mm neoprene drysuit for the last 4 years and has at least 300 dives on it and it is still in great shape and is going strong. She swears by it and I am probably going to go with a neoprene suit for my next drysuit.
Stay away from inexpensive shell suits constructed with an interior poly coating. This clear interior coating provides the water tight integrity for the suit but does not hold up well and will crack or delaminate in a relatively short period of time causing the suit to leak, usually in several places, and seam leaks are very common. It's a far better investment to spend a little more money on a full fledged tri-lam (nylon, rubber, nylon laminates) or spend similar money on a neoprene drysuit.
Whatever you get, fit is very important and a full and unrestricted range of motion with the heaviest underwear you will be using is critical.