tl;dr: The Novel
The novel affords Sophie more agency than the film, especially if you watch the film with the English dub, which turns Sophie into more of a passive traveller than the original Japanese does. I hope this is to do with the wish to basically sync syllables with mouth animations rather than some deep-seated desire on the part of Disney to keep girls in check, but you gotta wonder when you see what else Disney has produced over the years…
Here is an excellent breakdown of main differences between the YA novel and Hayao Miyazaki’s film adaptation, from a feminist point of view. Though both Miyazaki and Wynne Jones are known to be feminist storytellers, the feminism of the elderly Japanese man is quite different from that of the Welsh woman.
One thing the film did do though, was to broaden the audience for this otherwise obscure YA fantasy novel from 1986.