All just my personal opinion
Bach, St.John Passion BWV 245, with the following artists: Harnoncourt / Equiluz (1965), Jochum / Haefliger (1967), Rotzsch / Schreier (1976), Koopman / de Mey (1993), Suzuki / Türk (1998), Gardiner / Padmore (2003), Layton / Bostridge (2012)
Bach: Italian Concerto in F major, BWV 971 — Walter Gieseking (1940), Wanda Landowska (1933), Gustav Leonhardt (1965), Andreas Staier (1993), Ton Koopman (1986), Christophe Rousset (1990);
Bach: Partita in B minor, BWV 831, “French Overture” — Walter Gieseking (1950), Glenn Gould (1970), Christophe Rousset (1990), Andreas Staier (1993)
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)
Bach: The Motets — comparing recordings with the following artists: Bernius (2012), Christophers (1989), Gardiner (1980), Gardiner (2011), Harnoncourt (1980), Herreweghe (1985), Junghänel (1995), Katschner (2012)
Various Organ Works (mostly by J.S. Bach) / CDs, with Wieland Meinhold, Hansjürgen Scholze, Rudolf Scheidegger, and Ton Koopman
Bach: Cantata BWV 36, “Schwingt freudig euch empor” — Comparing 2 recordings: Koopman/Amsterdam Baroque Orchestra & Choir (2002), Lutz/J.S.Bach-Stiftung St.Gallen (2007, DVD)