Pairing Debussy and Ravel in their only string quartets is a cliche by now, and buyers have a wide range of choice. In terms of sheer virtuosity, no one has excelled the Alban Berg Qt., (EMI), who play with seamless technique and gleaming tone. but it all osunds a bit too efficient and impersonal. There's more atmosphere in the version by the Tokyo Qt., among others.
I listened to half a dozen recordings before settling on this one from the Quartetto Italiano (they were together for so long that you can get their historic mono recording of the smae music on EMI). The Quartetto doesn't try to sound airy, diaphanous, or particularly French. Instead, they give a presonal, uniquely phrased version that sounds as if each player is responding from deep feelings about the music. That's rare in performances of Debussy and Ravel, where the syle is more or less locked in. The miking is quite close, and although they lack the sheen of the Bertg Qt, the Quartetto Italiano deserve their reputaiton for making beautiful sounds.