Each solution has its advantages. Using the sun itself to track is good because it doesn't need to be calibrated, and it's portable. It accounts for atmospheric refraction, and earth's orbit eccentricity. I would worry about the challenges presented by rain, clouds, birds, and dirt. These are all probably manageable since the solar cells themselves need to be kept clean anyway.
I only suggested the calculation method because if you actually do know your location (most of us do) and orientation (compass), it doesn't require optical sensors. You don't need to feed huge tables into the controller; it's trigonometry.