Hi
"Best course"?
"Best system/agency"?
Becoming an instructor is fairly easy. Usually some 40 meters is the pre-requisite, usually meaning you have to master frenzel. Apart from that (assuming you are socially/mentally stable) it is just about paying the money.
If you haven´t done the levels, most agencies will fastlane you through this (since they want your money).
Which agency has the courses that are best?
Which agency will help you sell your courses?
Which brand is strongest?
No one can really answer this, freediving is still young.
Teaching beginners is a pretty straightforward business, where there are no real magic tricks, or superior systems.
I think most systems have a similar approach.
If you just want to get "a certificate", then choose the shortest, cheapest course.
If you want to become a good instructor, start of with diving more than 5 months.
Freediving students are .... how shall I put this... a diverse bunch of personalities... and understanding "who" they are and why they are there at the course is, according to me, essential - thus some psychology is useful. And the ability to improvise and use "the standard" in a constructive manner.
As opposed to scuba - there are situations where there are no universal answer.
"When shall I turn"?
"How much shall I breath before"?
"How much weight shall I have"?
These are questions no instructor manual will (or at least should not) give you one simple answer.
And this is why freediving instruction is so rewarding... for the instructor.
On the subject "what is a good freediving course" I have been thinking:
How to choose a freediving course
Sebastian