Thank you all for the further points. I am now undecided - is it ever so with photography! The first picture is more graphic, which in truth is how I saw the image. But as a portrait photographer I am seduced by the idea that face of the surfer becomes important too. Immediately after taking the picture, and bear in mind I was walking and shooting because I had seen the composition and had to remain at a constant distance from the surfer, we started chatting to the guy and I took down his e-mail and offered to send him a copy. It is of course a non commercial arrangement, but perhaps I am assuming he and his family would enjoy seeing more detail.
On balance to me the darker image looks more natural and the lightened one gives the impression the surfer knows he is being photographed, which he does not.
(Incidentally, in case anyone is interested in tech stuff, we had bought a new Panasonic 14mm prime lens and this was it's first outing - on a GH2.)