I'm certified through ACSM and the NCSF. Out of the two, NCSF has more practical knowledge - exercises, workout programs, nutrition, etc. ACSM is good in terms of recognition, but the whole test is basically anatomy and physiology. IMO you can know everything you want about origins, insertions, planes and axes, but if you can't teach someone a squat or a barbell curl in layman's terms you'll be a shitty trainer.