I've gone through a bunch of drysuits over the past 16 years. Some I wore out, others I didn't keep long because after I bought them I discovered things about them I didn't like ... so I got something else and sold the suit.
Number one thing to look for in a drysuit ... proper fit. If it doesn't fit you right, it won't perform to the best of its ability. Every other feature you can think of is secondary to proper fit. You should be able to get a full range of motion in the suit with minimal wrinkling and bagging, as these tend to trap air and make managing the air bubble in the suit less effective.
Other considerations ... front-zip or back? The trade-off here is that a front-zip suit gives you a sense of freedom in terms of not requiring help to get the zipper done/undone ... which can matter if you come out of the water needing to pee, and in a hurry to get your suit off. The upside to a back-zip suit is that the cut makes it easier to get a good fit ... and the zipper is generally less expensive to replace than on a front-zip suit (because it's shorter). This is something I put into the "personal preference" category.
Neoprene or shell? Again, trade-offs. Neo suits are generally more sturdy and provide some warmth (which means you could need less undergarment) ... but then, there's a big difference between a full neo and something like a crushed or compressed neo. The former dives more like a wetsuit, which means water pressure will tend to compress the suit and change buoyancy characteristics as you dive, while the latter is much less so. Also some considerations in terms of weight, drying time (a consideration if you're traveling and worried about travel weight). Shell suits are lighter weight, and dry much more quickly, but are more prone to leaks imposed by sharp objects like brushing up against barnacles or diving around wrecks. Depending on the suit, it can also be somewhat less easy to repair.
Seals ... neo, latex, or silicone. Again, each has its benefits and drawbacks. Neo seals tend to be sturdier and more comfortable, but more expensive to replace ... and less likely to find someone local to do it for you (or to do it yourself). You usually have to send the suit back to the manufacturer or some professional drysuit repair shop. Latex seals are less sturdy, but cheaper to replace ... and many people just do it themselves. I have no experience with silicone seals, so won't comment on those. Oh ... and I don't particularly care for the replaceable seals, although some folks like them. I find the neck seals less comfortable, due to the ring (and more expensive ... but you pay for the convenience of an instant replacement). And the wrist seals didn't work well with my dryglove rings ... although there are many different options out for drygloves, and some work better than others with the instant replacement seals. So it's a matter of making choices that are compatible with your other suit options and preferences.
There was an earlier discussion about pee valve, and I didn't notice that anyone brought up UTI (urinary tract infection). So I will. I had pee valves installed on three of my suits, as it was pretty much mandatory back in the days when I was doing a lot of deep wreck, technical and cave dives where I was spending hours in the water and doing a lot of mandatory deco. The pee valve is pretty much a no-brainer for that type of diving. But the trade-off is that there is always a potential for UTI, which is extremely unpleasant ... and can become quite serious. Unless there's a need for a pee valve, I wouldn't recommend it. If you're only doing recreational diving, I don't see the need for most "normal" people. I have no issues hydrating before a 60-70 minute dive and holding my bladder until after the dive's over ... and I'm an old man, so younger people could probably do it much easier than I can.
Oh ... another consideration ... boots. The usual choice is either built-in or rock boots. Both have benefits and drawbacks. The rock boot goes around an internal "sock" that is what provides the waterproofing. Socks work well enough, but can be prone to leaks at spots that tend to rub against the boot when you kick ... and you really don't want to walk around in them when not wearing the rock boots. Built-in boots are more convenient (one less thing to put on or forget to bring when you pack), but don't tend to fit as well as a rock boot will. They tend to allow air to more easily get into your feet ... which can be managed with minimal technique, but still more effort than a tighter-fitting rock boot. I personally prefer the convenience of the built-in boots. But some are less sturdy than others, and understand that replacement boots will cost a couple hundred dollars when they wear out, whereas replacement rock boots will cost you about half as much.
Also consider customer service. Some suits are well-made, but if they need repair they have to go back to the manufacturer ... and some are better than others for customer service. I had great customer experiences with some companies, and terrible experiences with others. The most notorious of the latter is (thankfully) no longer in business, despite the fact that they made a pretty nice suit. DUI is perhaps the gold standard for great customer service, but they charge accordingly (you usually get what you pay for). BARE used to be pretty bad, but they seem to have gotten a lot better over the past couple years. But if you send your suit to a third-party drysuit repair facility it's less a concern what kind of customer service the manufacturer offers.
Most of these things I just brought up really do fall into the category of personal preference, as do other things like pockets ... I always order my suits with pockets, so I can carry items like a DSMB or a spare mask (depending on the dive) ... or even an extra backup light. Only you can decide whether the utility is worth the extra cost.
... Bob (Grateful Diver)
