Assume that there are two computers which are connected with a copper cable, e.g. Ethernet. Also, there is a radio connection between them, e.g. AM radio, in order to exchange data. When we try to send data from one to the other, which one would be faster?  Assume they are the same distance away.

As far as I know, the propagation speed of electromagnetic signals in the air is better than the copper. On the other hand, frequency of the AM signal is smaller. Is there any other factors which affects the speed?