As LordCrash said, the Ranger is the King on the battlefield, you can do anything anywhere, almost any time.
Ranger's skill can't miss, Ricochet and Barrage can be devastating with the good weapon.

I find the skill Arrow Spray seriously lacking, but I knew it from the Beta and it was then the most overpowered skill I had ever seen.

As for Scoundrel, I agree that their skills are a little lacking, but the base Damage of a backstabbing rogue is astounding, especially with the Bully skill, just after a Trip.
To enhance the survivability, you can always give your Scoundrel a shield, you lose a bit of mobility & one chance to apply your eventual debuff with your weapon, and you gain blocking chance + stats.
There is no loss of DPS as you will do roughly the same damage in a single strike (hence the loss of chance to apply your weapon debuff, 1 strike instead of 2).

Mine is a Lone Wolf with a shield and Leech, and, to be honest, it's overpowered. I take less damages than a pure Warrior and deal 3 to 4 times the damage, with a huge mobility.