I think My Fairy King is their low key best song, it's the precursor to Bohemian Rhapsody and it's the song where Fred Bulsara became Freddie Mercury when he wrote the line "Mother Mercury, look what they've done to me." To which he explained to the rest of the band "Mother Mercury is my mother so I shall become Mercury."
But I do love Under Pressure and the story about how the song was created. How John Deacon came up with the bass line, went out for dinner and when he came back couldn't remember it until Roger remained him.
And how Freddie and David originally planned to record their vocals riffs separately without the other one knowing what the other recorded, and then they would mix their riffs afterwards. Freddie went first and started to riff, David snuck into the engineering room and made notes of what Freddie was doing. So the next day when the roles were reversed and David was doing his "riffs" Freddie went into the engineering room to have a listened and remarked to the sound engineer "this is amazing, I swear David is just a genius, just listen to how he knew what to do without even knowing it" to which the engineer said "I'd be a genius as well if I listened to what the other guy did too" to which Freddie shouted, "Oh what a rotten cunt!"