Willing vs. Forced

I like C, D and E.

I'm assuming C is by unaided circumstances/accident. An accident that results in a fun new experience makes for a happy ending for all parties, which helps when you try to associate with the other characters. I don't have it in me to do harm to someone, so I can't associate with the guy who shrinks/transforms women against their will, even if they do eventually enjoy it.

D is ok, they did it to themselves, and I can still associate with the people who come upon them. My greatest preference is a combination of C and D, where they bring the change on themselves, some mistake they make causes them to lose control of the change (stuck as the transformation/shrink, or a further transformation/shrink that makes them unable to change themselves back) but where they learn to enjoy it through the story, usually refusing to change back once someone finally is able to help them. I do like the poetic justice as well, though. Someone inventing a shrink-ray to zap her boyfriend and keep him as a pet, ends up getting shrunk and cared for by her boyfriend after the device irreparably falls apart and leaves her stuck.

E is my second favorite after the C-D combination I mentioned. Shrinking/transforming, having fun with your friend/lover, using your transformed condition to solve some crisis, then wrapping up with more fun with the friend/lover.