-- Last Updated: Dec-01-12 9:59 AM EST --
I must agree that in a good (meaning well-breathing) dry suit, the evaporative cooling effect is pretty strong. But *only* when you are soaking wet *inside* from sweating. If you are dry inside, there is virtully no issue. With a thick wet suit, you will sweat hard but you won't cool off either. You will sweat a lot in a dry suit too and you will cool off a lot when you finish. A non-breathing dry suit will work just like wet suit in terms of sweating you and not cooling you when you stop (of course, with the right layers assumed in both cases).
So, I must conclude, that if you stop active movement when soaking wet, a thick wet suit would be the better choice to keep you warm. Plus, leaks while in immersed in the water with a losely fitting dry suit can be a real trouble....
That said, for the kind of paddling I do most in the winter, a dry suit is better/easier to get in and out (in fact, I put it on at home, drive, paddle, wear it in the car back home - so pretty easy...