I'm always on the lookout for new materials and after a good deal of pondering, decided to give a Boston Valve a go.
This performed well in some pretty heavy surf today, including being bearhugged on a trip to the bottom, rolling under a very heavy wedge which I took on the head. The advantages are two-fold: firstly, they look pretty good. Secondly, the valve has two parts, a small cap for inflation and deflation on the go, and a larger thread allowing the whole valve to be removed from the mat for rapid deflation.
I particularly like the fact that it is a screw-cap design. No need to be tugging away on the mat.