Generally over the course of several fights Assassins/Rangers will have the best DPS. Whoever said bezerker does is kidding themselves, not trying to be offensive, but zerkers don't have near the damaging abilities that the scout line does, nor can they use poison.
Wizard/Warlock can out DPS the Assassin/Rangers in 1 or 2 fights, but use up a lot of power doing so, therefore they don't have the staying power. Assassins I think are the highest single fight melee damagers there are. Rangers beat them after about 3 fights due to the long timers on the high hitting Assassin abilities.
Swashbucklers and Brigands are close behind, and can keep the damage coming over the course of chain pulling.
This is just current observation mind, and might change in the end game, or when classes get hit with the nerf bat, and others get better abilities. Over all though most your DPS classes all compete with each other, just by doing it their own way.
"Never argue with an idiot, he'll drag you down to his level, and beat you with experience."