2 things that have been mentioned are important: the length needs to be over 2 meters (probably 3) for you to hear a difference. This is true, unless the equipment you are using has a fully balanced topology within it (as Mento refers to). If that is the case, then balanced will almost always sound better. Another issue which has not been mentioned is the environment. If you live in an area with alot of RFI and EMI, balanced will make a substantial improvement by just canceling out the noise that is picked up from these sources. This occurs because the 2 hot leads are out of phase. It of course does not eliminate all of the EMI/RFI noise, but it does reduce it significantly.
