I have been using a drysuit for ten years and have about 800 dives in them. I currently own two suits. Both are made by DUI. One is a crushed neoprene and one a trilaminate. I still prefer a wetsuit, but because of thermal issues that's not appropriate for much of the diving I do.
Things to consider in a suit:
1. Material. This choice will drive cost, comfort and durability factors.
2. Cost. Big range here. Somewhat correlated with quality. Definitely correlated with material. I don't believe the noise about drysuits being economical versus wetsuits in the long run. That's marketing nonsense. For a good drysuit, you're going to spend more money between purchase and maintenance than you would regularly replacing wetsuits. The issue is thermal. Cold is more than uncomfrotable. It's dangerous. Wetsuit heaters are a silly attempt to get around this.
3. Fit. Most suits don't unless you're shaped like a potato. Custom suits are more expensive. Some materials stretch and some don't.
4. Seals. Basically two choices-Latex and neoprene. Latex makes a better seal while neoprene is less vulnerable.
5. Valve positioning. While chest exhausts are increasingly rare, they're still around-especially on older suits. Avoid them. Inflator valves that rotate work and are a good feature. Ankle exhausts are a bad idea for various reasons.
6. Zipper positioning. Various styles. Some allow self-donning while others require assistance. Some are positioned better than others to avoid wear and stress. Across the shoulder types are particularly troublesome inasmuch as you need help to zip them, they get lots of stress across the shoulder and the tank straps rest on them which drives the zipper into your traps and puts weight on the zipper teeth. A new zipper will cost you 200-300 to replace.
7. Options. Things like pockets, boot styles, heavier grade latex on seals, p-valves (men only), attached hoods, zipper covers, valve positioning and dry hoods and gloves are options on certain suits. Just about anything can be changed after purchase even if the manufacturer won't.
I have clear cut opions about what works best. Send me a PM for those.