Well, the answer to that question is "it depends on the floorplan, and the lighting." If you've got an entirely separate lower level, i.e. its separated by a door, then its probably not as big of a deal as if the stairway leading down is open. My house has a stairway leading down to a hall way downstairs, so we used the same color of engineered hardwood downstairs as the real hardwoods upstairs. Now, if I had had a door at the top of the stairs or the bottom, I may have made a different choice in the lower level. One thing I would recommend- keep the floor finishes on levels consistent to make the space seem larger- i.e. if you use dark wood on a hallway, finish the rest of the floors on the same level the smae finish.

I tend to believe that the fewer flooring changes in the house, the better. Using the same wood would make the house feel consistent, but if there is a door blocking the transition then no you don't have to. Generally I would say yes, match them, unless it's a horrible color and you hate it.