We normally operate under the assumption that music is not comparable. Those that are in the musical canons, at least, in classical tradition, from Bach to Beethoven, Mozart to Schubert, Haydn to Mendelssohn, Brahms to Debussy, Chopin to Rachmaninoff, etc., each has their own way of writing great music. But subjectively, most of us admit that their is a rank in our preference as to who is a little bit greater, and I have discussed at length why Bach is among the rarest and greatest among composers. Beethoven is by no means cut short by that comment, though.
Pianist Andres Schiff made a series of lectures on the Beethoven piano sonatas. These are really great lectures with his virtuosic demos and deep insights. He maintains that the reason that Beethoven is a little bit greater than his followers, such as Schubert and Schumann, at least in Sonata writing, is that Beethoven consistently writes brilliant final movement of sonatas whereas they sometimes fall down in the works of others. To me, that is true to a great extent; but what I value Beethoven the most is his creativity, vision, unique character, strength, and a perfect combination of advances in techniques and in harmonic and musical languages.
I attended several concerts at UPF by the orquestra de cambra de la UPF, with pianist Pilar Guarne. She plays Mozart piano concerto no.13 with relative ease, but struggles a lot with the Chopin's Grand Polonaise Brilliente in E-flat Major. I can feel that Chopin is so much more difficult to implement physically in her playing. When I got home, I watched Yundi Li playing the Chopin piece, alongside Lang Lang, and I finally was able to answer the age old question: which one is a little bit greater?
Yundi Li was the winner of the prestigious International Chopin Piano Competition, and Lang Lang is a rather versatile pianist with a fantastic career globally. I used to think that once you reached that level of technique, you cannot really distinguish who is a little better, because a pianist who is able to mark himself musically (instead of technically), such as Glenn Gould and V.Horowitz, is rather rare. But this time I see that Lang Lang is a little bit superior than Yundi Li. Li played the piece without orchestral accompaniment. His playing is mostly sensitive and smooth, with great touch, but I can feel that he is not 100% at ease, and he did make occasional mistakes. But Lang Lang on the other hand, played with great ease, as if this piece if a toy piece for him. Indeed, that is a sure thing to expect when you see him handle Rachmaninoff concerti with such elegance and technical fluency. Chopin is an order of magnitude less complex.
Alas, I'm glad we had some answers.