Some things to factor in is the woods already in your home as well as the degree of formality and coloration of any wood furniture. The wood floor should compliment, yet be in a noticeable contrast to the wood stains used in cabinetry and furniture. Lighter floors tend to conceal scratches, dust and water spots moreso than darker stained floors. Some informative and tip sites esp. re. choosing the wood floor spieces are found here. Among other things, they address hardness to wood grain variations...
josie, we have rustic birch flooring and I still love our floor. I like that it is rustic as it has a lot of variance in the color. I also love the really dark flooring too but I've heard that it is a pain to keep clean.
Good luck in your choice and whatever you pick, I'm sure you will love.
****Look at objects not only for what they are, but for what they could be, vg****