Versions heard: I'd like to tweak this question to encompass all of the PotO fandom. I've read the original Leroux novel and the Susan Kay novel, as well as a couple incredibly shitty fanfiction sequels that got published. Out of the official recordings, I've heard/own the OLC, the OCC, the Vienna cast, the Dutch cast, and the studio version with Michael Heath and Kira Bronte. Phantoms besides the ones on the preceding recordings that I've heard/seen (not live, and most of them I've only heard sing a song or two) include Brad Little, Hugh Panaro, Howard McGillin, Peter Karrie, Steve Barton, John Owen-Jones, Earl Carpenter, Stephen Buntrock, Ted Keegan, and Tim Martin Gleason. Christines include Sandra Joseph, Julie Hanson, Elizabeth Southard, Lisa Vroman, Rebecca Luker, Rebecca Pitcher, Susan Owen, Amy Nuttall, Robyn North, Rachel Barrell, Deborah Dutcher, and Marie Danvers. I've seen the original film with Lon Chaney, the Robert Englund film, and the 2004 ALW film.
Why: Because it's incredibly pulpy entertainment that, at the same time, contains an almost indescribable complexity. I feel that the other versions border on becoming a huge cheese-fest or they tweak it to cater to females in the age bracket of 20-50 by focusing solely on an implausible romance between two, cardboard-cutout characters. The Erik, Christine, and Raoul of the Leroux novel have a depth that no other version has caught. (And I detest the fact that Erik is becoming a sex symbol. I do think he's sexy. But in the skeletal, no-nose, smells-like death sort of way).
Least Favorite: The 2004 ALW film.
Why: Three people. Joel Schumacher, Gerard Butler, and Emmy Rossum. Nobody really cares about the direction that probably made Hal Prince want to cry, so I guess I'll focus on how they completely stripped Erik of any plausibility. I hated him in the film, and I never thought it would be possible for me to hate any version of Erik. In the film, he was really nothing but a whiny emo bitch who really needed to get over himself. As well as go to jail for the murders he committed (I can't believe they actually showed him cold-heartedly murdering Buquet... what a mistake in the direction). Christine had the personality of a a piece of paper, though I will admit that it's not as if the stage musical gives her much of a personality either. What's essential then, is for Christine to at least have a phenomenal voice. I'm of the opinion that Emmy Rossum's voice is far from that (sorry for anybody who likes her). Patrick Wilson was good, though.
Favorite Christine: The Leroux Christine. My favorite performers for Christine are Lisa Vroman, Rebecca Luker, Rebecca Caine, Susan Owen, Julie Hanson.
Why: Lisa, Rebecca, and Rebecca for their beyond amazing vocal ability. Susan and Julie for their acting and their good but not amazing voices. Oh and I also really like Deborah Dutcher.
Least favorite Christine: Emmy Rossum. And, stage-musical wise, Sandra Joseph.
Why: Emmy Rossum because she hadn't had enough training for the role (being a part of the chorus in the Met as a child doesn't count). Her voice was weak, breathy, thin, and her technique drove me absolutely nuts. Her ToM cadenza was not a cadenza, she ruined AoM with her horrifying scooping, and... she really just isn't a true soprano, her high notes were screechy beyond belief. She is no where near the caliber needed to make her character believable. Emmy's singing "outdoing" Margaret Preece's (the woman who dubbed for Carlotta on the movie)? Doesn't make any sense at all! Sandra Joseph, I like as a person but... eh. She can, at least, adequately hit the notes (unlike Emmy), but her acting doesn't do it for me, and her voice is kind of blegh.
Favorite Phantom: Again, the Leroux Erik. My favorite performers in the role tend to follow/stay true to Leroux. My favorites are Hugh Panaro, Gary Mauer, Peter Karrie, and John Owen-Jones. Michael Crawford gets an honorable mention because he has some of the most extraordinary moments.
Why: Hugh and John simply for their orgasmic voices. I love Hugh's acting as well, he's incredibly sensual in MOTN but goes appropriately crazy and Leroux-ish towards Act II. Gary and Peter for their acting.
Least favorite phantom: Gerard Butler. Also, I think that Colm Wilkinson is a phenomenally talented stage performer, but his voice/acting just isn't Erik for me.
Why: Gerard... now, I don't put too much of the blame on him... because I think a lot of it was simply how the character was written and how the film was directed. Though, the man CANNOT sing. People who prefer a little rock 'n roll edge to a voice... by all means, look up Adam Pascal. He has that rough quality to his voice but he also can actually HIT the notes and he certainly doesn't make me cringe 10 times during a song he's singing.
Favorite versions of other characters: I love Carlottas of every form! She's much more interesting to me than Christine, and some of the time, I even think the performers who play Carlotta have lovelier voices than Christine. For example, I love Anne Runolfsson's voice much better than Sandra Joseph's. And of course Margaret Preece blows Emmy Rossum out of the water. And the Piangi of the stage version is awesome, especially that low sustained note during Il Muto. I also loved Nadir and his son from the Susan Kay novel.
Least Favorite versions of other characters: Ehh... I don't know. I'd say that the Raoul character from the Robert Englund film was grossly misrepresented. And it irked me how most of that film was spot on... except for the fact that Englund's Erik only wanted to possess Christine, not love her. Not to mention his creepy mask of choice.
Other stuff about you: I think I've already worn out my welcome :)