My favorite is Symphony #6. So dark and brooding. It's very unique among Tschaikowsky's own works.
And my least favorite...The Nutcracker. Tschaikowsky didn't like it, either. I think it's a pity that this ballet is more famous than the rest of his works. Oh, well.

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I stared at him wide-eyed for a few dreadful moments, thinking he had lost all sense of reality. Then I said to him, choosing my words with agonizing caution and reluctance, "Listen to Mozart, my young man."