Common versus uncommon. Which can be annoying. You try to retell "Tattercoats" and everyone thinks it's "Cinderella" -- except possibly a fellow panelist who also knows and likes "Tattercoats" -- better than "Cinderella", even.
And they get rewritten to put new messages in. Discussing what you can do with heroines. (which, in fact, I found a little annoying because it evinced a certain lack of knowledge about what a wide variety of heroines there were in the originals. "Kate Crackernuts" anyone?) I told the horror story of "Cinderella" being written as a temperance tract. That's the one that inspired Charles Dickens to complain about how we must respect the integrity of fairy tales. Which inspired talk about what we can and what we really shouldn't change.
How the most basic motifs of fairy tales tend to be the most stable parts. Everything else shifts about. Things like having things in threes last forever.
And nowadays, we aren't tell fairy tales as fairy tales, unless we are doing picture books. We write novels or short stories based on the tale. Folk tales are incredibly spare in style. You can cut off the heroine's hands and gouge out her eyes and be done with it in one sentence, and go on with the story. You can't really do that in a short story.
Different settings -- an audience member asked about and the other panelists were grave about the integrity and the culture and fitting it together. I was chirpy, because really, you're not doing anything that the storytellers of the culture didn't. One folklorist demonstrated that the publication of Grimms' Fairy Tales produced an effect on the fairy tales that were orally told in Japan. Storytellers don't parrot what was handed down to them from their grandmothers, but change all about. Some Victorian folklorists really didn't get that and described this or that motif in fairy tales as a survival from the Age of Stone..