The lower one does not expose the photocell to direct sunlight, which would eventually degrade the sensor and lens; has less chance of being falsely deactivated by stray light; and senses the overall light level in the area covered rather than light from a specific direction. All plusses.
The first one, properly mounted, will allow the controlled lighting to be as bright as daylight without tripping the photocell, as long as it comes from a different direction. A plus for that one.
