Final answer:
Beethoven's Ninth Symphony is likely his most popular work, noted especially for its 'Ode to Joy' movement, though the Fifth Symphony is also iconic.
Step-by-step explanation:
Beethoven's most popular symphony is probably his Symphony No. 9. This symphony is famous for its final movement, Ode to Joy, which is universally recognized and has been adopted as the European Anthem. While his Symphony No. 5 is also very well-known for its iconic four-note opening motif, the Ninth Symphony's influence and recognition, particularly the choral finale, often places it at the top of classical music rankings.