Thief of Time is probably his best, although I have a soft spot for Soul Music (but most of my friends don't).
Unseen wasn't great, but I am tempted by Sky's live-action version of Going Postal.
Tiffany fits superbly into the mythology of witches. Talking older than she is works because of her witchcraft (and is also influenced by Susan, granddaughter of Death, another magical older-than-her-years girl). Although my exposure to 9 year old girls has been limited in the past couple of decades I do know one that in adult company does demonstrate fascinatingly adult views and mannerisms. It's only when tired or with other children that she becomes a child again.
Bookmarks