Well, according to DUI's sizing charts I'm a stock large.
I tried a stock medium in the pool. It was ok, provided I never wanted to dive with heavy undergarmets. I could have literally never gotten it on though if I did - and that would be a problem. So I bought the stock large.
A "cave cut" is fine if you're going to dive only in caves around here where the water is 68-72F all the time. But most people who buy drysuits don't do that - I know I don't. I use mine in the salt of the gulf in the winter, where it might be in the mid 50s, and then I use it in springs, which is the usual 68-72F. If I can't put that second layer of underwear on, its useless, and I ain't buying two suits. So I live with SLIGHTLY big (to fit the bigger undergarmets....)
The NexGen doesn't fit too badly, provided you get the right one. The NexGen I had was a stock size and fit me ok - until I lost 30lbs! THEN it fit like a potato sack - but that wasn't due to the suit, it was due to me losing a bunch of weight. So I sold it.
Fit is EVERYTHING on a Drysuit.
As for DUI's leaking, the stock low-profile exhaust valves indeed do. I've had the DUI folks tell me otherwise, but 15 minutes in the pool, emerging with a sopping-wet left arm, closed their yaps, and I got my suit with the high-profile Apeks valve, which DOESN'T leak. IMHO DUI ought to quit putting those pieces of junk on what is otherwise a wonderful piece of kit.