How important is carpet warranty when determining which to pick?
From what I understand, carpet warranties are all but useless. They have so many conditions that it is effectively impossible to actually make a warranty claim. For example:


You must have your carpet cleaned professionally every 16-24 months. You need to produce receipts showing a professional company came to clean this frequently since installation
Stain resistant warranties not covering non-food/beverage stains, such as caused by animals or cleaners
Other limitations on stain warranties, like "there can be some slight loss of stain resistance in high-traffic areas such as stairs (and hallways, in front of doors). The warranty excludes any residual stains that my occur in those areas."
Warranty may only cover replacement of the affected area (so say a 5x8 area is affected, they'll just cut out and replace that bit), and may not even be 100% - apparently they can degrade, so after say 3 years, they'll only cover 60% of the cost. They won't replace your entire carpet because there's a problem in one small area.
Warranty may not cover labor after some period of time. Worse, you may be forced to use a specific installer at whatever rates they charge (thanks, shirlock)


I have no direct experience trying to get warranty on it, but because of all of this, I would put very little faith in the warranty numbers. If you can never effectively never file a warranty claim, they may as well offer a 25 year or even lifetime warranty. What's it matter - if you were 2 months late having your carpet cleaned 4 years ago: warranty voided.