You also have two main materials to choose from, each of which helps give a certain design aesthetic and comes with certain benefits.
Plastic: Plastic, usually of polycarbonate, is a very common lighting fixture material. A basic plastic can work well in casual spaces. However, there are ornamented plastic styles for more regal or upper-class looks. Dark-colored plastics give a modern and sleek look. Because the recessed lighting is way up in the ceiling, it will be hard to notice that the lighting is even plastic. Plastic is also a good way to keep the cost lower.
Metal: Metals can give an austere look that is great in modern or industrial spaces. Steel is a very common material to find for its durability, as is aluminum because of how lightweight it is.