Of the two, I would go with ACE. Personally, I never heard of ISSA. I have mine through the NSCA (CSCS). There are other good ones out there also. I included a link below where you can check to see if an organization is an accredited certifying organization. I keyed in ISSA & nothing turned up – not a good sign. You can’t go wrong with ACE. Good luck Clint.
I own a Personal Training Company. ACE has come a long way over the past 10 years. I have hired several trainers with both certs. Personally, I prefer NASM, but that wasn’t an option. 🙂
My next preference is ACE. ACE takes into consideration, not only the body, but the entire person. Personal Training is about building relationships with the person and helping them correct postural issues. You need to correct the foundation before you can start adding the frame. ACE understands that. They also understand that are emotional human beings and have to learn how to make fitness a priority.
I also do not care for ISSA’s approach to nutrition. Although the information is 100% correct. When dealing with the average person, it’s best to start out with very simple instructions. Once they can master that and create a habit, then start adding more. You wouldn’t put a kindergartner in 5th grade math, right? It’s all a building process.
Hope this helps!