Luthien If you haven't already decided, and having read both, I would definitely say Witchlanders. It's more suited to younger readers and reads almost like a fairy tale. That's not to say it's "dumbed down," but if you're eleven, it's the one to choose!
Christina i searched up the other book and although I haven't read neither I am more attracted to the witchlanders. They both look very interesting but I am a more fantasy person , if you prefer romance over fantasy go for the sweetest dark but if you enjoy fantasy go for witchlanders. If I were you i'd read both of them.