I've studied this topic thoroughly so I'll give my two cents.
The old Rubatex was indeed the most crush resistant and also had the most long term spring back/recovery benefit of any neoprene known.
Unfortunately the original Rubatex USA company went out in 2002, but then the name was bought out by another company but the material wasn't the same. I don't know if they're even around anymore. I just saw Bob's post above regarding Wetwear, so maybe they are?
I was using a suit builder down in Long Beach, CA (Don at M&B Wetsuits) and he actually went to the Rubatex plant and bought up everything they had thinking he'd have a lifetime supply and he ran out in a few years. I got one of the very last suits ever made from true Rubatex.
So that sent builder looking for another source of something similar and he stumbled upon a company out of South Korea that makes a very dense material for commercial use. It's actually more compression resistant but it's also incredibly stiff. He had all sorts of other materials of varying densities, probably 12 different choices from several different companies including Yamamoto and their entire line plus all the clone companies out of China making something close to Yama but not quite.
So bottom line, if you want to make sure your getting something special you almost have to order one custom made by somebody that knows materials very well and has access to all the different options out there. Just because somebody is a custom suit builder doesn't mean they know what they are using. Many times they'll just use what they can get and what's cheap without really knowing what it is.
Most commercial scuba suit companies will shop around and get material that is the best bang for the buck without much regard for long term material stability. Good material is expensive. The cheaper stuff uses a lot of nylon in the blend to keep costs down but it also very spongy and crushes down easy, and the really cheap stuff stays crushed, sometimes even after one really deep dive it won't fully recover.
There is a tradeoff, the more compression resistant the material both short and long term will also mean a stiffer material and not as soft and spongy and harder to move in.
So generally speaking, if you see cheap suits on sale to ridiculously cheap it means they are that cheap for a reason.
As far as specific brands of suits in the 5 mil thickness, I would suggest going to a freedive suit in the $600+ range of a reputable brand.
There is even variation in freedive suits too, not all freedive suits are created equal. I bought one below $400 and thought I was getting a good deal, but found out it crushed down big time at depth and I got really heavy (not good for freediving!). I found out later it was a Chinese made Yamamoto clone with a cheaper and inferior blend. However, freedivers are more fanatical about suits and materials used, so generally freedive suits will be better quality than off the rack scuba suits. The sellers also seem to know more about what they are selling.
When I was at the shop buying that suit I looked at one that was denser and nicer but was also over $700. Looking back that's the one I should have bought. The salesperson even warned me about it but at the time price is all I could see.
