Raster - renders your views as raster images, resolution depends on your output quality setting (Document setup>Paper). The highest setting produces 300 DPI (black linework might still look a bit jaggy)
Vector - renders your views as vector lines and flat colour areas. When printed to paper or viewed on screen, the image is always rendered in the highest quality supported by your device. This is the best setting for line drawings and the like, but vector rendering doesn’t support textures, shadows, transparency or other raster-based effects.
Hybrid - renders your faces as raster images, with textures and shadows, and overlays them with the edges ans profiles as vector lines. It tries to combine the best parts of the two others.
Anssi