On a 1998 Philips CD, number 456 574-2, the Guarneri quartet plays both of Leoš Janácek's string quartets:  the 1923 "Kreutzer Sonata" and the 1928 "Intimate Letters".  This is wonderful music, tonal but not staidly so, beautifully played (in 1996) by the Guarneri.  Plenty of melodic and harmonic beauty, deeply felt but not sloppy or over-the-top.  Excellent recording captures the rosiny, woody aspects of string tone, and a bit of astringence but not too much.  Good acoustic ambience...fairly reverberant, but the sound is very clear.  Possibly more closely-miked than is completely realistic, but that gives a clear insight into the separate lines without sounding glaringly close up.  I don't know the other recordings of this piece, so can't comment on which others one might entertain in addition to, or instead of, this one.  Doesn't really matter:  this is essential music, beautifully rendered.  I will say no more except that every music lover would be well-advised to listen to these pieces, in this or some equally good recording if one exists, and to go hear them live if the opportunity arises.

Sorry for the lack of correct Czech diacritical marks.  A computing issue I will work on.