Is that I don't actually have a very good ear. They do those "name the singer" bits on the Met matinee opera quiz, and I never even get close, despite having listened to opera my entire life. Maybe that means it doesn't really matter which recording I get.
One tries to read the reviews on Amazon, but, as you say, there's so much subjectivity that it's a mess. You get people giving the same recording 5 stars and 1 star, on the merits!
I just thought I'd see if anyone back here had a favorite: it's sort of a niche and a long-shot. I will check out the reviews, those sites are useful.