It depends on where you work and what your emphasis is.
Physical therapy/kinesiology based: NASM’s stuff is the best mainstream stuff
Strength and conditioning and physiology based: NSCA’s stuff is the best mainstream
I know a lot of different certifications so let me know if you have more questions for something specific you may want,.
Check out the over 200 courses, approved by up to 16 certification agencies, on IDEA’s site: http://www.ideafit.com/fitness-education.
I think the best continuing education course for personal trainers is the course that brings the personal trainer closer to his or her professional goals.
If the professional goal of the personal trainer is to work with older adults, then the best choice for that individual personal trainer would be something related to the older adult population. Hopefully the course would expand upon his/her current knowledge base.
I don’t think there is one good CEC course that fits the needs of all personal trainers.
There are two ways to look at this question. You can get closer to your specialty or bring up weak areas in your training knowledge.
I prefer to use Exercise Etc and DSW Fitness as my CEC providers because it is convenient for me as there are no conferences held in Alaska. Also I hold multiple certifications so it makes it possible to “double dip”(gain CEC’s for more than one cert at a time).