The esthetics and performance of carpet is similar to the fabric in your clothing. The type of fiber used, the construction of the cloth, and the color all play a role in the styling, cost, and performance of that garment.
Nylon
Nylon is a durable fiber that has good resiliency and good stain resistance. It is a strong fiber, which makes it suitable for the heavy traffic of a commercial area or active household. It is typically more expensive than olefin and polyester based carpet.
Polyester
Polyester fiber has some of the most beautiful textures and colors available, and is durable and resists wear. It is susceptible to crushing, but has excellent resistance to stains. Most polyester-based carpets have a luxurious feel (hand) that people love to dig their fingers into.
Olefin
Olefin, also called polypropylene, is a relatively inexpensive fiber that has good stain resistance. It's color is added before it is made into a fiber, and thus has great resistance to bleaches or fading caused by sunlight. However, it has poor resiliency, which means the carpet may eventually show signs of crushing.
Wool
The most expensive of the fibers listed here, it is a natural fiber with moderate soil and stain resistance. It has durable, luxurious "hand", reduced visible soil due to fine, light-scattering characteristics.