Copper vs. Aluminum

Agree with Mattax.
Solder & brass are poor conductors of heat, but a necessary evil in the construction of copper radiators. The benefit of the alum is that the tubes can be made wider 1.00" or 1.25", versus 1/2" for copper. Better heat shedding fins can be used with the alum. The overall result is that the alum rad is better at cooling.