Mendelssohn sounds closer to Beethoven (more repetitive, simple melodic), light, cold.

Chopin sounds more romantic: either more dark or more dance. Piano pieces sound more technical, fast, rolling, tender.

Beware that piano pieces of both composers sometimes sound song-like.

Chopin has solo piano and piano concerto.

Mendelssohn has everything else and does not have piano concerto. (Chopin, Mendelssohn)

Schubert sounds more classical, light,

Chopin sounds more romantic: either more dark or more dance. Piano pieces sound more expressive, technical, fast, rolling, tender, sometimes song-like.

Only Schubert has piano song, piano quintet, piano trio, string quartet, symphony.

Only Chopin has piano concerto.

Only piano pieces are difficult to guess. Both composers have slow piano pieces, while Schubert usually keeps clean and clear melody and sounds more uniform. (Chopin, Schubert)

This is an interesting comparison of two romantic piano composers.

Chopin generally sounds more uniform, regular, repetitive. Other pieces sound very simple romantic.

Rachmaninov sounds more brutal, flexible, sweeping. Also he uses some russian melodies.

Chopin has only solo piano and piano concerto here. (Chopin, Rachmaninov)

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...)

Basically, Chopin is a poet and Beethoven is a warrior. Beethoven's Diabelli Variation appears often (probably it occupies a large portion of the database). Although such late works of him contain rich drama and tension which may trick you into into choosing Chopin, they can still can distinguished from the latter by their Beethovenian solemnity and willpower, dry texture and grey harmony, whereas Chopin is always sentimental and poetic, with his delicate grace notes and bouncing up-and-down development of melody (much funnier and fancier than Beethoven's), fluid texture and colourful harmony. (Beethoven, Chopin)

Chopin and Verdi seam easy to guess on this island, while you can spend much time trying to separate JS Bach, Handel and Telemann. How do you distinguish Telemann? (JS Bach, Chopin, Handel, Telemann, Verdi)

Mainly piano. Janáček is more folklore. Chopin is tender and technical, more melodic and handsome. (Chopin, Janáček)

Being both Romantic composers, Beethoven is closer to classical music, being more strict and repetitive. While Chopin is tender romantic, expressive. Probably most difficult will be to compare their piano pieces. Chopin does not have vocal, chamber and symphonic works in this game, mainly piano and piano concerts. (Beethoven, Chopin)

Chopin is usually considered to be more tender and feminine, while Liszt is more energetic, masculine, dry, technical, window-dressed. Also you can hear something Gypsy in Liszt melodies.

I'd be glad to hear more helpful recommendations on this island! (Chopin, Liszt)

Chopin is romantic and tender. Stravinsky is modern, unpredictive, folklore, rhythmic. (Chopin, Stravinsky)