These are the most reputable by a mile. Others are more or less a mail-order cert that’s not much more than a money making scheme. I’m sure there’s an exception or two, but I don’t know them personally. NSCA is THE standard when it comes to being a college and above level strength and conditioning coach. ACSM is gaining some ground, but ACSM has in the past been almost exclusively an add-on cert to PT, ATC, etc. I think ACSM had the PES (performance enhancement specialist) letters behind it for a while if my memory serves me right.
A previous boss wanted the core of us who worked in the college’s fitness center to get personal training certification. She figured we’d learn a lot and it would be useful. She did a lot of research and felt AFFA or AFA (can’t remember if there were one of two Fs) was a reputable organization and it would meet our goals. We went through a weekend course that was brutal. All we learned was how to do an initial intake with a BS few standardized tests, and anatomy. The biggest waste of my time ever, and that’s saying a lot. People asked several times how to put a program together for clients. The response every time was “it’s the personal trainer’s responsibility to learn that on their own” along with an eye roll. The teachers’ response to safely perform some lifts was equally non-existent.
Look up NSCA and ACSM. Alternatively if you’re strictly interested in kettlebell stuff, try talking in-person to some local trainers.