Reflection is an interesting wave phenomenon that occurs between waves on the electromagnetic spectrum (EM spectrum). It depends of the smoothness of the interface the wave is reflecting from and the color of the material in the interface. Both materials you have chosen work well as far as color, in terms of reflecting and not absorbing the light. Aluminum foil is harder to get to be a continuous smooth surface. Once you take it off the roll and try to apply it, it starts bending; it is very difficult to not have a reflecting surface that is very multi-faceted with aluminum foil. For this reason, I think the use of DVD-CD material as a chosen medium to reflect light waves would provide a stronger, more focused reflection of light. If one could get the aluminum foil to smoothly apply to a backing with some rigidity, it might provide superior reflection results. But until that happens, I would go with the DVD-CD material.