I have tried many different types of string on my classical and, whilst agreeing with Don Firth,can reccomend D'addario "Pro-Arte"(composites).These include an extra G string(composite)which may feel a bit plastic by comparison but seems to solve the old G string problem especially when amplifying.At about £10 a set,they're a little more expensive than some but have a great tone and last well.I love to pick up my classical after a long spell of steel stringing,it's tones are more subtle and your playing develops more expression as a result.