I would say Demi Lovato because she have an amazing voice and a lot of experience. However, if they search someone that can handle being a celebrity pressure I would say none of them because they all changed to "fit in the box" or they had problems that being famous kind of caused or aggravated. Yes Miley's good but I don't think she could be a good judge, plus Simon Cowell seems to search to be the mean judge, Miley is saying the things like it is and it can seem brutal. Avril has a lot of experience but I think her voice isn't so deep enough to teach to some apprentice how to sing a particular note, that's my fear. Fergie's good but... I don't know, I just don't see her as a judge.