Which PT certification would you suggest? There are so many to choose from.

Consider where you want to work and who you want to serve and how you want to serve them. If you have a mentor or role model, ask. Do some research into clubs and studios that offer the standard of service you want to be branded or known for and ask about what they require or like to see in applicants. That will get you started.
At our club we preference ACSM, NASM, NSCA and ACE – preferably beginning with PT and going on to the Advanced cert. More than likely if you continue in the industry within three years most trainers I’ve worked with have two certs under their belt; so don’t feel you can make a “wrong” decision. You’ll just be making a first choice!
The certification isn’t necessarily your learning experience; it’s your proof of the knowledge you have and then you’ll be learning practical ways to apply in with continuing ed workshops and conferences, articles, webinars, and experience.
Good luck!