Favourite world?
Mine was the Immortal world, where there was no real children, and all the people wore old victorian style clothes, and they had mechanical servants and mechanical children. They were also immortal, and were hundreds of years old.
This was the most exciting world, IMO. I loved how they wouldn't let Kathy go because she was the only real child in the world, and the adults were going crazy over who got to keep her.
Plus, the mechanicals were kinda creepy in a cool way.