I've been told by folks working rebuilding radiators that the aluminum ones tend to have problems with the tanks leaking. Of course they say all the failures all day long, so that may not be a good sample.
However, our trucks bodies do flex a lot, I was contemplating putting an AL radiator in mine, but decided against it just in case it flexes enough to cause problems. An AL radiator will cool better, but as long as the cooling system is in good shape and not overloaded, copper/brass will work fine.