Cut pile carpets are loose on top, there are two basic types with hundreds of options in between, the first being more formal with a dense velvety smooth finish and the other a more casual and textured looser finish.
The more formal carpeting is a solid color which will show footprints and vacuum marks, being that it's a smooth, solid finish it may not be the best option for high traffic areas.
The more casual textured carpets, hide footprints, vacuum marks and stains because of their color and variety of length. They're Both quite durable.
Loop pile carpets on the other hand feature yarns that are looped on top. In the loop category there are level loop and high-low loop varieties. Both are very durable in high traffic areas.
Loop pile carpets are very tidy looking, they don't show vacuum marks or footprints. On the downside, you may not want loops if you have children or pets with claws because if you catch a loop it can unravel.
You can also find cut and loop pile carpets. Which combine the two other types, it can give you a lot more variety with texture and pattern. Because of the changes in tone and length this type of carpeting can more easily hide wear and stains.
When you're choosing a carpet, don't forget the padding. it insulates against temperatures and noise; it will also help the carpet wear better.
Pricing is as diverse as choices, just make sure that you compare apples to apples, one store may just price the carpet, while another may include padding and installation. I'm Mrs. Fixit and it's just that simple!