All just my personal opinion
Beethoven: 6 Variations on an Original Theme, WoO 77 — Ronald Brautigam (2010, fortepiano), Olli Mustonen (1995); Beethoven: Allegretto in B minor, WoO 61 — Ronald Brautigam (2010, fortepiano); Beethoven: 6 Ecossaises, WoO 83 — Alfred Brendel (1985)
Beethoven: Variations on the Minuet “à la Viganò”, WoO 68 — Mikhail Pletnev (1997), Olli Mustonen (1995), Ronald Brautigam (2011); Mendelssohn-Bartholdy: Organ Sonatas op.65 — Heinrich Gurtner (1989), Stefan Schättin (1995)
Beethoven, “Eroica”-Variations op.35, Comparing recordings with the following artists: Artur Schnabel (1938), Glenn Gould (1970), Svjatoslav Richter (1970), Emil Gilels (1980), Konstantin Scherbakov (1984), Alfred Brendel (1985), Olli Mustonen (1993), Ronald Brautigam (2010)
Beethoven, 12 Variations on “Das Waldmädchen”, WoO 71 — comparing recordings with the following artists: Emil Gilels (1968), Vladimir Ashkenazy (2006), Olli Mustonen (1993), Ronald Brautigam (2010)
Ludwig van Beethoven: Bagatelle “Lustig und Traurig”, WoO 54 — comparing recordings by Ronald Brautigam (fortepiano, 2010) and by Olli Mustonen (1996)