Hmmmm. tough question. I am fond of the tried-and-true Arpeggione Sonata of Franz Schubert, but I eat, drink, sleep, and practice by J. S. Bach Unaccompanied Suites. C P E Bach Cm concerto takes first place for its drama and beauty, and the melodies in Mozart Sinfonie Concertante are simply divine. Actually, anything played on viola is beautiful with good intonation and that wonderful, relaxed vibrato that makes the instrument just sing….ahh….one day…..