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

All songs are unique, or should be.  Except those that are plagiarised, which is many.

By the way, 'most unique' is not a useable expression.  'Unique' means that there is no other item the same.  A thing is either unique or it is not.

OP should have written 'most unusual' or suchlike.

Not a song, but it must be John Cage's 4'33"

https://www.youtube.com/watch?v=yoAbXwr3qkg