FFS! Just buy the full set of books, read them and learn the contents. That means reading them whenever you can. It really does not matter which series of books you choose just learn the contents.
Don't skimp, learn them thoroughly. Get to the point that you can answer every question in the back bit and every question in the confuser without any errors.
It aint just a question of passing the exams, it is the underpinning knowledge that will help you.
