Don't know Isokoski. Lott and Schwarzkopf are both fantastic, but very much in the 'old diva' style. I haven't heard those particular recordings, but Bonney's version is simple and lush. I would guess that the other two are not, but I could be wrong. That's not a knock on them, I'm just guessing that it's a completely different style.
Morgen
Richard Strauss' 'Morgen'. The most beautiful song in history? Check out Barbara Bonney's recording.