While it is debatable whether we should even have this as a separate category, and certainly it is used somewhat haphazardly, we are covered because our Mob template ensures that all Quest NPCs are also listed in Category:NPC (Mob Type).
Quest NPC should be used only when the NPC in question does not respond, or at least not in a way other than Ambience, unless you have the quest he is involved with. This does NOT include Quest Givers.
Pages in category "Quest NPC (Mob Type)"
The following 100 pages are in this category, out of 100 total.