Well that is kind of a hard question. There is no best class, only the best class for you (kind corny, i know). If you are a melee person looking for damage dealt, Berserker or Assassin might be something to look into. Both have a high damage output. Assassins rely on evasion to stay alive, attack quickly, and can have a very high critical hit rate. Assassins are good for PvP for quick and deadly attacks. They can hide from players and sneak attack. The right combination of criticals can take down most people in no time. Berserkers have a little more variation into how i can be played because it can equip swords, axes, hammers, duel wield, and use 2 handed weapons. They have a higher armor class than assassins and more health. This is what brings their advantage in PvP. They can survive a little bit more in a fight and still have a high damage output. As for Ranger, they have little melee ability, but can be devastating at a distance. Their PvP prowess is mostly for sniping the magic classes out before they can turn the tide. Against melee classes, they will lose if they can't distance themselves.
In general, a character is as good as its equipment. I think this game has very nice balance in the damage dealing classes. The decision is up to you what to be and how you play it. Hopefully this will help and is all accurate. This is just what i have noticed in my gameplay.