I’ve acquired a number of certifications over the years, all of which have their strengths and limitations.
First, if you have a degree, get your CSCS. The exam is tough, the material is basically good, and there isn’t much BS that you have to “unlearn” later (what there is is largely confined to the nutrition component). Plus, the CSCS is recognized around the world and was designed for post secondary grads and that certainly helps from the “street cred” end.
No degree? Well, the NSCA CPT is OK, but a lot more fluff than the CSCS. Reeeaaal easy.
Next, I strongly advise getting some type of Poliquin certification. It isn’t “perfect” either, but at least you learn how to execute exercises perfectly, which when you boil it down is what people want to hire you to do in the first place.
Finally, and this is more important than all of your certifications combined, OFFER TO JOB SHADOW WITH A REALLY GOOD STRENGTH COACH. After working with normal business type clients for years, I had the opportunity to assist an excellent strength coach with training football players, hockey players, and MMA fighters for 50-60 hours a week. It kicked my training chops up to a new level.
All the theory is fine, but its in the trenches where you really learn.