I took and passed them both and I think they seemed essentially the same. There were some questions on both that stumped me, across categories, but not a lot. The only major difference that stood out to me was that ANCC did not provide normal lab values and the Academy did. They were not really that helpful in context b/c the ANCC provided plenty of other information in the question that would clue you in even if you didn't know the lab values.
I attended a review course and used a book, and reread chunks of assessment text from school, reviewed developmental milestones/psychosocial stages, etc. I studied by system for the month prior, up until the week just before, during which time I did not study at all. I took the final week off and just relaxed. I don't believe in cramming, lol.
My review book's recommendation was to keep taking the practice tests until 80-85% proficient.
I'm a good test taker, but not everyone is. I was so surprised when a physician preceptor I really admired and respected told me he failed his Family Practice Boards the first time! The test doesn't define us! Study, do your best, and if at first you don't succeed...