I previously held a performance enhancement specialist and corrective exercise specialist certification from NASM (before PT school). I have a pretty extensive background in personal training and would like to use some of that experience in a job. I spoke to a lot of practitioners about the CSCS. My interpretation is that many PTs don't know about those other certifications very well. But most ortho PTs know about the CSCS. It's a common one in our field where the others are still specific to personal training. I decided to go for the CSCS just to establish a common language in the field of PT. I didn't find the information in the course to be different from my other certs...so knowledge one, I think either would be fine. But for PTs, you may have more acceptance of the CSCS (this may change in the future). From the personal training world, I do know that CSCS is considered to be the toughest exam...most people can't pass that exam after taking a weekend personal training course.
I took the exam midway through my 2nd year of PT school and it did not require a lot of studying for me.