Mozart sounds more classical, clear, structural, repetitive.

Mendelssohn sounds more romantic, expressive.

Only Mozart has clarinet concerto, flute concerto, piano concerto, clarinet quintet, horn quintet, string quartet, requiem, horn concerto. (Mendelssohn, Mozart)

Mozart sounds more regular, classical, transparent.

Schubert sounds more romantic. Some Schubert piano pieces can be slow.

Only Mozart has clarinet concerto, piano concerto, flute concerto, violin concerto, horn concerto, horn quintet, clarinet quintet, messa, opera.

Only Schubert has piano trio, piano song. (Mozart, Schubert)

This is a nice starting island. But some of composers will be harder to guess. (JS Bach, Beethoven, Chopin, Debussy, Glass, Mozart, Pérotin, Rachmaninov, Tchaikovsky, Vivaldi, Wagner...)

I found it easier to distinguish these by simply checking if there are elements of Mozart in the music or not. He is always the same, whereas Dvorák can be different, but will never use most characteristic Mozart elements. (Dvorák, Mozart)

Very interesting island, having two well-known composers. Mozart is classical, but very melodic. Beethoven is romantic, but very structured and most of his melodies are simple and developed from previous melodies. Chamber works can be most difficult to guess. (Beethoven, Mozart)

These two classical composers sound close. Mozart sounds more prepared, natural, airy and beautiful. Haydn - repetitive, sudden changes, eccentric. (Haydn, Mozart)

Both composers are light and melodic. But Mozart is more classical, while Dvorák is more romantic. (Dvorák, Mozart)

Very simple comparison of two most known classical and late romantic composers. Mozart sounds even (often funny and airy). Wagner - broad and dramatic. (Mozart, Wagner)