We use what is most commonly used in our area, but I think knots is probably the most recognized wind measurement world wide.
I live in the US and there are thousands of anemometers at airports, marinas and iwindsurf.com locations for us to check before heading to the water. Most in MPH, and some in knots, but I think most US sailors can convert MPH to knots in their heads with reasonable accuracy. When most of us in the US say it's blowing 20 knots, you can be sure that that's observed or estimated based on multiple area reading.
No reason not to be as precise as possible.
I don't see Beaufort used often, so I don't have any idea about the conversion to something I know, so I would have to look it up like the majority of windsurfers (just a guess).
I think knots for wind speed and water craft speed is the standard for all things nautical, at least for most of the world (inland lakes in the US may be an exception).
I am glad that windsurfing is in the metric system, I just wish the US government would also convert. Too many politicians afraid to make waves. As they say "Just Do It".
Formula 160; iSonic 111; HiFly Move 105; Tiga 263; '85 Mistral Superlight.
Maui Sails TR 11.0; 9.2; 8.4; 7.6; 6.6; Maui Sails Switch 6.0; 5.2; Maui Sails Global 4.5; 4.0.