WHAT IS THE MOST UNIQUE SONG THAT YOU HAVE EVER HEARD?

Modern Music by BeBop Deluxe. It's a short suite that takes you away and brings you back

Very unique Vangelis Papathanassiou’s 1972 take on Revelations in the Bible Title “00”, Aphrodite’s Child 
not as unique as Chopsticks 

Cats in the cradle for sure.  Honorable mention would be blinded by the Light. Imho.  Cheers Dick H. 

"tomorrow" [from "Annie"] played and sung by  Major "mule" Holley and "slam" stewart, on string basses. the unique part is that major holley was a human contrabass and could and did sing in unison with the strings of his string bass, all the way down to low E. it is a weird effect, he demonstrated it to frank sinatra and it made frank grin broadly at the novelty of it. 

Anything by the Dixie Dregs