ACSM,NASM or NSCA foe cpt?
I say none is better than another. All of those provide solid educational material. What will make you a great trainer after you get certified is YOU!
Like Brick said, at the end of the day, the individual cert doesn't matter all that much in terms of getting a basic trainer's job. I was certified through the ISSA and they actually got me my first job in a gym by contacting a local manager who was also certified by them.
This article from Tim Henriques breaks down a few of the ones you mentioned though.
I know absolutely nothing about certs, but that won't stop me from chiming in. Let me give this a shot.
Which of the certs mentioned have the most widespread recognition? Which of the certs are percieved as "the best" by clients? Is one cert more advertised than another? Which cert is going to help a trainer sell themselves?
Client's don't know a rat's ass about certifications.
All three of those are high quality and recognized by employers.
NO cert. will help a trainer sell themselves considering people don't even know about them or what they stand for.