Good question Mud.
I have all 3 now, having just bought waders a week ago.
Firstly none of them keep you warm. Some of them keep you warmer longer than others.
Dry suit keep you warmest the longest because you wear thermals underneath, and stay dry.
Wetsuits second longest then waders.
There are different types of dry suit.
Some are made from neoprene (like wetsuits), there are many other types, trilaminate, rubber, coated fabric and combinations of all
Three.
The Neoprene in drysuit's is normally crushed:- 8mm crushed down to 4mm so you get loads of neoprene insulating you from the water, but surprisingly heavy.
Great for diving in cold water, heavy and cumbersome on land.
The zips on Neoprene suits are super heavy duty and cost about $200 to fix, they were designed by NASA.
The best type of suit for most people in cold water is a neoprene suit. Most people would advise this type, but having thought about your particular situation I wouldn't.
Are you crazy you may say,
but no!
I would advise you to buy one of the Baggie material trilaminate ones.
The benefits of this material are:- light weight, dries very quickly, light, easiest to put on. You can also put it on up to your waist, and wear a belt to walk in to where you want to detect.
Which ever dry suit you get after its on and zipped up you open the dump valve and squat down to force as much air as possible out of the suit. If you're going deeper than waist you might need some weight, you will be very buoyant no matter how much air you squeeze out.
One of the dangers with a dry suit is that if your feet get higher than your head you will be floating upside down, and it's not easy to right yourself, so you can drown. it's easy to stop, that's why a course is a good idea for divers. Ankle weights (made out of your found sinkers) not heavy but some light weight is an idea. OBN said about the straw down the neck, to let the air escape, it sounds like a good idea, I've never tried it though...
You can vary your undergarments to suit the conditions.
You must try the suit on before you buy it, check the zip, wrist and neck seals and make sure the boots are nice and thick soled for hiking in. Make sure there are no tears in the suit! Take care in that cold water buddy, we need you on here! Cheers WW