All just my personal opinion
Beethoven: String Quartets — summary for comparisons of recordings, involving the following ensembles: Alban Berg Quartet, Amadeus Quartet, Artemis Quartet, Brooklyn Rider, Busch Quartett, Chiaroscuso Quartet, Emerson String Quartet, Endellion String Quartet, Guarneri String Quartet, Hagen Quartett, Kuijken Quartet, LaSalle Quartet, Leipziger Streichquartett, Melos Quartett Stuttgart, Quartetto Italiano, Quatuor Mosaïques, Takács Quartet
Beethoven: String Quartet op.135 —comparing recordings with the following ensembles: Alban Berg Quartett (1982), Amadeus Quartet (1963), Artemis Quartet (2011), Busch Quartet (1935), Emerson String Quartet (1997), Endellion String Quartet (2005), Guarneri String Quartet (1969), Hagen Quartett (1990), Hagen Quartett (2012), LaSalle Quartet (1976), Leipziger Streichquartett (1998), Melos Quartett (1984), Quartetto Italiano (1968), Takács Quartet (2004)
Beethoven: String Quartet op.132 — comparing recordings with the following ensembles: Alban Berg Quartett (1984), Amadeus Quartet (1962), Artemis Quartet (1998), Busch Quartet (1937), Emerson String Quartet (1997), Endellion String Quartet (2005), Guarneri String Quartet (1969), Hagen Quartett (2003), LaSalle Quartet (1973), Leipziger Streichquartett (2001), Melos Quartett (1985), Quartetto Italiano (1967), Takács Quartet (2004)
Beethoven: String Quartet op.131 — comparing recordings with the following ensembles: Alban Berg Quartett (1984), Amadeus Quartet (1963), Artemis Quartet (2002), Brooklyn Rider (2011), Busch Quartet (1936), Emerson String Quartet (1997), Endellion String Quartet (2005), Guarneri String Quartet (1969), Hagen Quartett (1999), LaSalle Quartet (1977), Leipziger Streichquartett (1994), Melos Quartett (1985), Quartetto Italiano (1969), Takács Quartet (2004)
Beethoven: String Quartet op.130 — comparing recordings with the following ensembles: Alban Berg Quartett (1983), Amadeus Quartet (1962), Artemis Quartet (2009), Busch Quartet (1941), Emerson String Quartet (1997), Endellion String Quartet (2006), Guarneri String Quartet (1969), Hagen Quartett (2001), LaSalle Quartet (1972), Leipziger Streichquartett (2006), Melos Quartett (1985), Quartetto Italiano (1969), Takács Quartet (2004)
Beethoven: String Quartet op.127 — comparing recordings with the following ensembles: Alban Berg Quartett (1982), Amadeus Quartet (1963), Artemis Quartet (2010), Busch Quartet (1936), Emerson String Quartet (1997), Endellion String Quartet (2008), Guarneri String Quartet (1969), Hagen Quartett (2004), LaSalle Quartet (1976), Leipziger Streichquartett (2001), Melos Quartett (1984), Quartetto Italiano (1968), Takács Quartet (2004)