Mountain bikes are designed for several different riding styles and terrain. You will need to figure out what type of riding you'll be doing most of the time. Is it smooth trail riding, cross-country racing, all mountain cruising or lift accessed gravity mayhem?
Test ride as many bikes as you can in your price range and riding style category. You will find that some bikes will just feel right while others don’t. The more bikes you ride the better feel you will have for what you like and what you don’t.
Kevin Tisue, 2013