My problem with the idea of making the demons the good guys is that I would have to make them good! Demons are inherently evil, which sort of precludes the idea of them being heroes (other than inadvertantly). I can see the attraction of a story seen from the perspective of the evil villains. There is a dark side in everyone's nature that would empathise with the nature of the villain, but if I made the demons truly demonic, it would require a set of readers who wanted to see things the way a demon would. I'm not sure that there would be many who could really identify with this way of thinking. I'm sure I wouldn't.