I'll be honest and say that I'm not completely sure what you mean by this question. Things likes "Great Shift", Wizards" or (lol) "mothers" (I guess you are referring to a situation where your mother is the cause for a change) or something else are "tools" for me, "universes" as often called.
When your question refers to the usage of those I can say that I like the Great Shift the most. This universe gives you a definite setting of event and you can deal with the results.
That leads me to the other interpretation of your question: What I personally like for myself in all this TG fantasy?
Again, the Great Shift describes it best. I love being a man, but the GS would force me having to live a completely different life from one moment to another. The exciting part for me is how those situations could look like, how I'd handle them and where this would lead me .... that's where my fantasy sets in when I think of TG stories. :)
I hope I answered your question good enough. But I also would like to ask this of everyone else:
Which fantasy does you lead through the TG community?
Is it a fantasy like mine, to simply see how another life is like on the other side of the gender fence? Is it the fantasy about living our your female side by reading about crossdressing because you also do it in real life? Or what curiosity is it?