USATF Certs:
If you want to coach US National teams. Example: The Junior Women's Throws at the World Champs. Take these courses every summer, and get up to level 3, and you will be among the group selected to coach at those events. You can have nice certifications on your office wall.
USTFCCCA Certs:
If you want to be a college coach, rise among the ranks of your peers, and earn lifetime achievement awards by the USTFCCCA, then these are the certs to get. Also good if you plan on being a general worker for 15+ years and want to kiss the behind of the Director of Track/ XC at a D-1 school.
Lydiard, Bowerman, Igloi, etc never had certs like the above branches have today. Heck, I doubt Vigil and Larson have certs. Most of the best coaches are D-2 + D-3 (sometimes NAIA + D1) coaches who have to take the time to develop the moderate talent that they have with the limited resources.
Bottom line in today's NCAA/ High School world, better get 1-2 certs to stay relevant and make it look like you know what you're doing, even if you don't. Go with whichever one your institution will pay for, and whichever one is closest to your home.