I used Remote Pilot 101. Been studying off & on since June. Took the test today and scored 95%. It really does depend on how you learn. Jason's videos were bite-sized and covered what you need to get a solid understanding of the fundamentals as well as pass the test. The purchase also entitles you to re-certification use of the course along with updates every two years. There are courses that are more in depth but there is a balance between getting a masters degree in FAA regulations and learning what you need to pass the test and properly operate a SUAS for commercial purposes. Conversely I suspect some can watch a few videos, take a few practice exams, and pass the test without gaining much appreciation of what is needed to safely and legally operate. No doubt there are a few who could read the Pilots Handbook,
Pilot’s Handbook of Aeronautical Knowledge ,and pass with flying colors. Most, if not all, of the material is presented there. So, it really depends on what you need to best learn what's needed.