First, the type of wood. Brazilian Cherry seems to be the newest fad in flooring, and it's one of the hardest woods out there. But, it comes from a very wet climate, and so in Colorado, it tends to shrink more with the lack of humidity which causes cracks between the planks. It also fades easily, so if you place furniture or a rug on it, pretty soon you will see a difference in color.
Oak and hickory are the most recommended for our area because of the dry climate. They're fairly hard, though not as hard as cherry. But they take stain well, and retain their color better (though they will still fade some.)