I use the heaviest gauge copper wire zip cord the hardware store sells. I have yet to have someone demonstrate any other cable sounds better. They all say they can hear a difference, but no one has proved it in a double blind test. Maybe soon. I am running some very powerful amps and they do just fine. YMMV
Oh, yes, I have some very big Monster cable speaker wire, pure copper, and all the other marketing stuff. They look a lot nicer.