Pine. On the opposite side of the hardness scale sits pine, which is technically not a hardwood at all. Pine is a soft wood, though its hardness varies wildly with the species of pine used. If you're buying a pine floor, be sure to find out what kind of pine it is.
Pine is a character wood. It has pin holes and knots and it's popular for that reason. It's difficult to keep it looking pristine, which just adds to its character.