The different positions have different advantages.
Helmet cam: cool because it's a paddler's eye view. But you need a) to keep your head as still as possible and b) remember to scoop water over the camera every now and then to clean the spots off.
Deck cam on foredeck facing backwards: pretty cool view point, better if it's angled slightly away from the paddler. Lens self cleans as the nose dips in the water.
Mast cam: mast mounted on rear deck. Issue is that the lens gets covered in drops and the salt stays behind as it dries. Not such a problem in a decent downwind. The mast has to be very securely attached to the deck so that it doesn't whip about.
Deck cam facing forwards from the rear deck: most boring viewpoint in my opinion.
Clip with bits from the first three viewpoints:
Rob
Currently Epic V10 Elite, Epic V10 Double.
Previously: Swordfish S, Evo II, Carbonology Zest, Fenn Swordfish, Epic V10, Fenn Elite, Red7 Surf70 Pro, Epic V10 Sport, Genius Blu, Kayak Centre Zeplin, Fenn Mako6, Custom Kayaks ICON, Brian's Kayaks Molokai, Brian's Kayaks Wedge and several others...