Just wanted to present u the farm route that i currently do during the halloween event, which i think can be quite effective.
Im farming Black Lion Chest Keys with a new created Warrior ( Choose: Human Warrior Common Folk when created and at step 8 Hospital). Ur done with the lvl 10 personal story step at lvl 4. In the middle of the route i take a step into the halloween portal in queensdale and farm the 2 bosses in the labyrinth (Center and South East Corner). Even with low lvl you have a chance to drop lvl 80 exotic armors there.