I think the copper ones work fine. But Mark brings up a good point.
Let's look at the science;

Aluminum vs. Copper

Copper has a better heat coefficient than aluminum, so you may ask why racing radiators are made from aluminum. It is about more than just the weight. Logic would dictate that you could make a radiator out of copper and it would be smaller, and consequently lighter, than an aluminum radiator due to the better heat coefficient. The real reason is that copper radiators are not all copper. They have a good percentage of lead in the copper that makes up the radiator core. This lead acts like an insulator and impedes the radiator's ability to reject heat. Another reason is that the braze material covering the copper as part of the core manufacturing process also impedes the heat transfer process.