NASM and all of the certifying organizations do a very good job with individual prep materials. I am assuming your question really is about choosing the level of prep material you should purchase. Ask yourself a few questions.
1. Is price an issue? If so, does your budget answer this question?
2. How much background in exercise science do you have? If you already have a good understanding of anatomy, physiology, biomechanics, etc. then you don’t need as much study material. And vice versa, less knowledge equals more study material.
3. Are there things in any of the packages that you think you won’t use? No sense buying things you feel you won’t actually use.
4. How much time and effort are you going to invest in the materials? If you think you will enjoy more study material and it fits your budget, purchase the package that offers you material to fit your study plan.
I tend to purchase the bigger packages because I just like to learn and like mulitple formats for learning. I consider my education to be the most important part of being a fitness instructor. And my business includes instructor courses, www.hawiifitnessacademy.com . I don’t offer distance learning, especially for teaching new instructors or fitness clients. I want to make a living, but I don’t teach solely for the money.