That's a rather cruel question to ask, because it's so difficult to choose one among all these master pieces.
I adore Music of the Night (for me it's Erik's love serenade) and Phantom of the opera with the same force especially if they are sung by Gerry or Ramin Karimloo.
Next I would say Point of no Return because of the passion, lust and desire that it inspires (also with Gerry or Ramin).
I have a little fondness with Stranger than you dreamt it when Gerry sings it. We saw him so sad and disillusionned as he speaks of his hope, dream and how he sees himself. No one would listen is also a heartbreaking song that I like...
Then I would say that Wishing you were somehow here again, Angel of Music and Down once more final trio close the ranking.
You see! Impossible to choose!!!!