All just my personal opinion
Mozart: Adagio & Fugue in C minor, K.546 — Hagen Quartett / Chiaroscuro Quartet;
Mozart: 6 Variations for Piano & Violin on “Au bord d’une fontaine” in G minor, K.360/374b — David Oistrakh, Paul Badura-Skoda / Petra Müllejans, Kristian Bezuidenhout
Bach: 4 Duets, BWV 802-805 — Ton Koopman, Christophe Rousset; Bach: Chromatic Fantasy & Fugue, BWV 903 — Wanda Landowska (1933), Andreas Staier (1988), Christophe Rousset (1990), Ton Koopman (1986)
Beethoven: Great Fugue op.133 — comparing recordings with the following ensembles: Alban Berg Quartett (1983), Amadeus Quartet (1962), Artemis Quartet (2011), Busch Chamber Players (1941), Emerson String Quartet (1997), Endellion String Quartet (2006), Guarneri String Quartet (1969), Hagen Quartett (2001), LaSalle Quartet (1972), Leipziger Streichquartett (2006), Melos Quartett (1984), Otto Klemperer/Philharmonia Orchestra (1956), Quartetto Italiano (1969), Quatuor Mosaïques (2016), Takács Quartet (2004)