I'm cutting and pasting some of this from a reply on another thread cuz I'm lazy like that:
I wouldn't bother with anything but NASM or the NSCA. NASM has an excellent methodology for client eval and exercise progression, and the NSCA is a continuous leader in research and practical information in strength and conditioning. The ACSM used to be very good, but I'm not too sure that I'd recommend it anymore for a "general" personal trainer (I'd still go to them for special populations work and exercise physiologist in sub-acute care and cardiac rehab settings). None of the others are terribly good at preparing an individual for training (the majority of them just copy what the ACSM says, anyway...I've seen the materials!).
Of course, in the end a certification is a piece of paper that says that you passed a test. It says nothing about your ability to motivate and safely prescribe exercise. I've known some trainers with excellent academic backgrounds in ex sci and impressive certs that were horrible trainers, and I've also known trainers with little academic background and "average" certs (ACE) that are outstanding trainers. Although the recognized quality of a professional's cert
does imply that given trainer's commitment to his/her field and knowledge (IMO), it is ultimately still what you make of it...Learn, practice, read and research, and you'll be better than the rest.
And for the record: Looking for NCCA accreditation is a good place to start, but having said that, ACE, ACSM, The Cooper Institute, NASM, NCSF, NETA, NSCA, NFPT are all accredited by the NCCA...in other words, it doesn't really matter (in terms of knowledge gained by the certification process) because being accredited doesn't mean anything in terms of the materials presented or required for certification. You can put a pretty yellow and blue NCCA ribbon on a personal trainer certification, but a crappy cert is still a crappy cert.