Windrunners originally had my vote. Being able to fly would be the single greatest ability as far as fun goes. But Windrunning seems to lack practicality. Sure, they are incredibly mobile on the battlefield and can reach distant battlefields quickly (although teleportation as a surge would be even faster.) Edgedancers, though. A well trained edgedancer can't be touched, even by a blade. They are the ultimate assassins since no wall could hinder them, and i'm sure that since friction doesn't apply to them they make very little, if any, noise when the move. They can also act as field medicss with their Regrowth surge. Lift was able to bring her friend back to life, and his throat was slit. Edgedancers would be ideal medics, since they could float through the combat "like a ribbon on the wind" finding wounded allies, healing them, and then dancing away. They can also grow food for troops with their Growth surge. They even seem to be gifted as innately nimble and quick.
Flight is awesome, but I have to give Edgedancers the 'edge'