Balanced (XLR) or RCA cables?

Does anyone know what are advantages of using XLR vs RCA cables? I am thinking of using XLR from my digital source to preamp and from my preamp to amp. Does it matter if the components used are tubes vs solid state when considering between xlr or rca?
Xlr's carry a quieter signal especially on long runs and sometimes its connection will have a higher gain than the RCA. It is usually not as advantages unless your whole system is connected this way, ie, music source component. It also really depends on the equipment being used. Some sound much better with xlr and some with rca - you need to try each before puttuing out more money for xlr. Some components are true balanced for XLR while others just have an XLR connection.
I think it's important to emphasize what Ljgj has already stated: that an XLR cable does not necessarily a balanced connection make. Lots of components have XLR connections without having fully balanced circuitry. And without fully balanced circuitry from input to output both all along the sonic chain as well as within each component, one is as likely to be adding non-musical artefacts to the signal rather than removing them. This is because the signal will have to be converted to single-ended and/or back again and any such manipulations usually add something to the signal. Having said that, so far I've found excellence of design and build quality to be more of a predictor for good sound than presence or absence of XLR connectors. As always, if you already have the capability, it's worth a try, especially for long cable runs. dr.joe
To learn everything you need to know about balanced vs. unbalanced see Rane Technical paper #110 at It is the most informative article I have ever read on the subject and is MUST reading for anyone with a ground loop. Rane also makes a great unit called a Balance Buddy that converts unbalanced inputs/outputs to balanced inputs/outputs. If you need long interconect runs (> 3 meters) and dont have balanced input/outputs it is the way to go. Cost about $220 wholesale.