i'd use copper. Copper have the best conductivity of the 3 and fairly ridgid.
Fixed:laugh: Although I would choose stainlessThe thing that does worry me about the copper is the fact that it can oxidize if not protected properly. This distribution block/rail will be in the engine compartment, copper does offer the best conductivity but in this case it would be better to use aluminum or stainless steel.
As mentioned above, I think the only place that would be a concern is in the actual connection point. Which after connected, the area would be air and water tight not allowing any chance of oxidation in that critical area.The thing that does worry me about the copper is the fact that it can oxidize if not protected properly. This distribution block/rail will be in the engine compartment, copper does offer the best conductivity but in this case would it be better to use aluminum or stainless steel.