Definitely all 3. The main advantage is that OEM HID projectors have a specific beam pattern and cutoff so that you get the most out of your headlights and don't blind other people on the road. As a bonus, they look very sleek and clean, and are by far more reliable than plug and play kits. However, due to cost and skill required, projector retrofits are sometimes out of reach for some (including me). I just went with a high and low beam HID kit for my stock headlight housings. There is some glare, and there is definitely no distinct beam cutoff, but the added light on the road and brighter blue-white color is very nice. And paired with my yellow fogs, they look amazing at night.