There are many different options for garage door materials out there, each one suited to different weather conditions, home styles, and personal tastes. You can go for steel, wood, aluminum, glass, or fiberglass, or a poly-blend of more than one of these options.
But one of the most popular and versatile materials commercially available for garage doors is fiberglass. Fiberglass is pretty much the best of both worlds- they don't dent very easily, and they can be formed to look like wood without the weaknesses of a an organic material.
However, keeping up fiberglass garage doors requires some work. Small things that you casually overlook one day can later turn into a real problem. If you notice your wheels sticking, spray them with a special graphite compound to keep them lubricated. Inspect screws and hinges from time to time to ensure their structural integrity. Check to make sure there is no water pooling or running along the door, which can warp or damage fiberglass garage doors if left too long.
When cleaning your fiberglass doors, (which should be performed fairly routinely to upkeep them) clean in and around the tracks as well as on the surface and around the edges. The best and cheapest cleaning agent to use is a solution of water and vinegar, which are fairly effective in cutting through dirt and grease.