Two quests that you MUST do :
Each time, you'll get to choose between two weapons with quite different stats. So do both to get both kinds...
For Witch hunters, get the pistol from one and the sword from the other.
Unmasking the enemy (pretty easy)
Check the rewards here : Unmasking the enemy.
Starts in Caledor (Tier 4 elf area) in the south west of the map (24.5k, 78k) at the camp (speak to Erindrel Quickleaf).
Faith is madness (pretty long and some harder bits)
Check the rewards here : Faith is madness.
Starts in Chaos Wastes, to the south of the map.