All four sang or played on many other’s records, but just a few guest musicians appeared on a Queen song (+ a handfull of demos).
Who would you like to have heard on a (what?) Queen song? Would it be an improvement?
I think a duet between Freddie and Annie Lennox would have sound great! It’s a hard life or Play the game would be my choice.
I would love to have heard a collaboration with Prince, although with the egos involved there I doubt it would have happened. One that I think would have worked well was Ann Wilson of Heart....something really rock and roll!