Nylon - Still one of the most durable fibers the stain protection has to added the fiber to prevent from stains.
Polyester - Naturally stain resistant. Has very vibrant colors that you can't get in nylon.
Triexta - Very durable, most stain resistant fiber with 0% absorption rate. Similar durabiltiy as nylon.
Olefin/Polypropylene - Very stain resistant except for dirt usually found in inexpensive berber carpets. Usually for the budget-minded customer or temporary use. Commercial carpet, very low pile and tightly woven.
Wool- Expensive fiber. Cool in the summer, and warm in the winter. Does stain easier than most fibers.