This question is pretty easily solved with an application of the Right Hand Rule. If your thumb points in the direction of motion, and your index finger points in the direction of the magnetic field, then the other finger point in the direction of the force.
So, the magnetic field of the earth goes (roughly) in the north-south direction. You would want the wire to move in a direction perpendicular to the field lines to maximize the effect from the field. Additionally, you'd want the electrons to be at one end of the wire, at a maximum distance away from the other end. So the wire would lay along your "force" direction finger.