I was just looking up the best way to hook up a new Marantz pre/pro and 5 channel amp. It turns out there is a measured ~12 dB difference in S/N ratio with the RCAs coming out on top, that's because the Marantz gear is not balanced, it just offers the ability to use balanced cables which are processed back to single ended. So it really does depend on the component in question, it's not always better to use balanced connections and in home environments the noise rejection usually does not matter. But if your gear is a balanced design then it's usually best to use XLR cables.