I must confess that I have a "love/hate" relationship with waders! I love them when they keep me dry. I hate them when they leak! Currently mine keep me dry. I am not sure what brands Mark will have available, but I would suggest to him that buying mail order is a bit risky, going into an outfitters and trying them on is a better approach. If you are going to buy mail order then a chat with the company over the phone for advice is probably a good idea. I guess Mark will be looking at lightweight breathable waders as opposed to neoprene. Breathable waders are meant to let sweat out but not water in. Neoprene waders provide insulation as well as keeping you dry, they are ideal when fishing in very cold water for say grayling in the UK or winter steelhead in the USA.
When you are able to try waders on in a shop then you need to try sitting, bending and kneeling in them. You need to be able to do all those moves without feeling restricted. Wearing waders that restrict you is tiring and they wear more quickly at the pressure points. I tend to prefer stocking foot waders, but then you need separate wading boots. I prefer stocking foot waders because the waders roll up as a smaller package and you can keep the boots (which get dirtier) separate. Also the boots take longer to dry. The other advantage of stocking foot waders is that my float tube turbo fins fit straight over the stocking feet and I don't need the boots on when float tubing.
All waders should come with a belt which you tighten around your waist to trap the air below the waist so if you get swept away you can bring your knees up wrap your arms around them and float. The idiot above (yours truely) wearing Orvis waders has not remembered to put his on! A water proof pouch is useful for car keys etc. I like built in gravel guards (flaps that pull down over the top of your boots) as well. The gravel guards also seem to stop the boot laces coming undone. Some of the latest wader types are designed to be rolled down to the waist when it gets warm, but I have not tried those.
I think I am on my 4th set of lightweight waders having had a variety of brands (Hoggman, Orvis and currently Redington). Waders are subjected to all sorts of wear and tear (hopefully not tear) as you walk through brambles, climb over fences etc so ideally they need to be fairly robust. Seeing what the fishing guides are wearing is a good indicator as long as you bear in mind that they probably got them at a discount or for free!
Finally, if you want to make your waders last, treat them with respect, don’t leave them wet in the back of the car for long periods or near hot surfaces. Hang them to dry naturally both internally and externally.
I bet there of lots of things I haven't covered so feel free to comment, I still have lots to learn.