Many good suggestions here. It's also the case that the 3rd book you read on a topic often makes more sense than the 2nd, and 4th more than the 3rd. Understanding is cumulative, so it's not a question of "which" book, but "how many".
I remember finding sometimes on my journey that I'd open a book and think "well, I can't make heads or tails of it." Then a few months later I'd try again and in the meantime I'd have read simpler ones and then the difficult book had become approachable.
