Nylon - A durable fiber that is ideal for high traffic commercial or residential applications. Resilient and soft - Nylon is a pricier choice though it withholds its longevity.
Polyester - Well known for its vibrant array of colours, Polyester is a more cost effective fiber. Incredibly hard to stain and in the case that you do happen to stain it is easy to remove.
Olefin - A lesser durable fiber that is hard to stain and will not fade when exposed to sunlight or chemicals.
When deciding what carpet is best for your home remember that all fibers can be constructed different ways. In a heavy commercial area always consider Nylon the way to go. Perhaps even in a residential high traffic area like a living room or family room. In low traffic areas like bedrooms or basements a polyester or olefin will perform and and will be more cost effective.
The Big Myth
Some consider carpet to be a 'BIG NO NO' for a household with someone that has allergies to dust. Though unlike hard surfaces, dust gets trapped on the carpet until vacuumed away whereas dust sitting on a hard surface has the chance of going airborne when disrupted.