It’s an awful question to pose, to pick just one (or even several). I’m forcing myself to limit myself to five:
- The 2nd movement of the Ninth: a dialectic of nostalgia and dissolution, of wistfulness and nihilism.
- The 1st movement of the Ninth: an astonishing accomplishment both formally (everything is in the first two bars) and emotionally: a full symphony in itself, suffused with resignation and struggle.
- The Andante movement of the Sixth (though they’re all amazing): all that is great and lofty about passion and sorrow.
- The scherzo of the Fifth: music to create universes by (and watch them perish as quickly as they materialised).
- The 1st movement of the Fourth: a joyful, lilting, classical-sized whirlygig (and again, a great formal construction).
If I’d allowed myself 10: the 3rd movement of the First; the 3rd and 4th movement of the Second; the 1st movement of the Third; the last movement of the Ninth. (Or of the Third. Or of the Sixth. Not easy….)