certified personal trainer

if I am a certified personal trainer what is the best fitness company to work for?

what is the best national gym chain to work for ?

Avoid national chains, they pay their trainers a very small portion of what they charge for personal training sessions. They can and do charge anywhere from $50-$100 per session and usually pay the trainer anywhere from 25%-35% of that charge. Usually smaller private studios pay a higher rate (50%-60% of session charge) and don’t impose high sales volume pressure.
A chain like Golds, Worlds, NYSC, etc are good for a little bit of experience but a small private studio will pay the best.