I have been a bodybuilder for about four years and I am thinking about going into personal training. Which certification is the best?
I personally think the ACSM (American College of Sports Medicine) is the best if you are in the states. Its a bit more expensive than some of the others and its harder to get but worth it in my opinion as it is very well respected.
Any of the above certifications will be fine. Most all gyms will accept any of them when you are applying for a job. Your clients won't know the difference, the smart ones just make sure that you are certified.
From a practical standpoint. Choose a cert that has a lot of information on subjects you need to learn more about. Acsm-clincal. Nsca-sport performance. Nasm-functional. That way you get certified and bring up a weak area.
Don't expect any cert to be ground breaking training information. They are meant to show competancy in the field, not label you as a professional.