I've mostly used Apophysis rather than Chaotica. But that's probably just a personal preference.
Chaotica is good for rendering fractals. It uses all processor cores and thus the rendering takes much less time.
Apophisis is a bit more user-friendly in term of creating (programming, drawing) fractals.
Chaotica is under active commercial development right now, and Apophysis didn't change much since version 2.09 (September 2009).
You should visit the Aposhack chatroom
and ask people there.
I haven't used made fractals for quite a while, so I'm not aware of current situation with Chaotica and if it is already more user-friendly than Apophysis.
Cheers and have fun making fractals!