The only carpet in our new home is on the top floor. It keeps the bedrooms cozy and it cushions footfalls so the people in the kitchen or living room below don't hear you stomping around.
We chose carpet that would match our dogs' hair. In fact, it will match ANY dog's hair. After years and years of sweeping the floors at Manning Dog Training, I discovered the generic color of all dog hair when mixed together: heather gray! So that's the color we sought. The "heather," which usually has some subtle brown tones in it, allows for slight variations, as opposed to a solid, flat color that would show any dirt or off-color hair.
We also chose nylon over wool. It was about a third the price, was said to actually wear better, and be much more stain resistant.
As for the texture, we chose a cut pile. Berbers are very popular these days, but we were afraid a dog could easily catch a toenail on those loops, which would cause snags in the carpet and potential damage to the dog's feet. Same thing with any type of looped pile. The cut pile we bought is fairly dense and lush, but not so dense that is shows every track from dog paws, human feet, or vacuum cleaner.
If your idea of a good carpet is one that doesn't show dog hair, holds up well under lots of paw and feet, and doesn't cost an arm and a leg, get a heather gray nylon cut pile. Interestingly, the style of the pattern we picked is called "No Nonsense."