When looking for a personal trainer, all too often people go by looks and nothing more. If a trainer looks fit themselves, they must be the best, right? Maybe. Maybe Not! Just because someone looks fit and in shape, doesn't mean they know all there is to know about helping you get that way. They may know what you need if they have studied exercise physiology, but they probably just have great genetics. We all tend to have a body type similar to our ancestors. If your family is thin, you are very likely to be thin. If your whole family is morbidly obese, you aren't going to be able to achieve a six pack even with the best of education in the fitness world. Some trainers are fighting bad genetics and hereditary diseases in order to maintain their health even if they have a little bit of a belly.
So, if you can't judge a book by its cover when searching for a personal trainer, what do you need to look for to get the most bang for your buck? Education! The American College of Sports Medicine (ACSM) is the premier certification that most other certifications model their programs after, so anyone with an ACSM certification would be number one on the list to use as a trainer. Some of their certifications require more education than others. The CPT (Certified Personal Trainer) is the lowest on the totem pole because it doesn't require much education. Their clinical certifications are better quality and require at least a bachelors degree in an exercise science. These clinical certifications are specifically so that these trainers can work with clients who have specific illnesses, diseases, or previous injuries causing limitations.
The National Strength and Conditioning Association (NSCA) also offers a CPT that doesn't require a degree. Their more advanced certification is the Certified Strength and Conditioning Specialist (CSCS), which requires a bachelors degree. This organization is more focused on athletes instead of the clinical populations. Therefore, this is the certification that is required for the strength and conditioning coaches for most collegiate and professional sports teams.
Either of these certification organizations would provide the most education among trainers. Other organizations, such as the American Council on Exercise (ACE), the Aerobics and Fitness Association of America (AFAA), the National Association of Sports Medicine (NASM), and FiTOUR all offer certifications in personal training and group exercise which are widely recognized by many gyms, but do not require a degree in exercise science. Some of the trainers from these organizations are more educated than others depending on how much they have studied on their own. While these organizations give them the basic knowledge to work in a gym, they do not give them the education to work with special populations or prescribe dietary plans. Be sure you check what other education they have that qualifies them to meet your specific needs.
Bottom line, if you have clinical issues, you want someone with an ACSM clinical certification. If you are an athlete or want to be an athlete, you want someone with an NSCA CSCS. If you are generally healthy and just want general fitness without dietary recommendations, any of the other major certifications are fine (and the trainer may be less expensive). If you ask a trainer about their education and they aren't proud to tell you what organization they are certified with or where they went to school, they probably don't have the knowledge to give you the results you want or need, so please continue your search for an educated trainer.