Consensus on this board is that "it is not the agency but the instructor that matters." To me this statement is indicative of the fact that training agencies are a global failure. The whole purpose of a certification agency is to create and maintain a certain standard across the board. Imagine how silly it would sound if someone said, Harvard, MIT, Oxford do not matter. Look for a good professor instead.
While there may be some truth to this, it certainly is far from the full story. One of the reasons instructors matter, irrespective of agency standards, is simply how well they can teach and whether their style meshes with that of the student. You can have an instructor that holds a high, stringent bar, but if they are not patient or unable to explain concepts well, the student will not get much out of it. As a college professor who has trained and worked at various institutions throughout the country, the idea of looking for a good professor(s), instead of an institution is not silly at all. In fact, when it comes to graduate training, this is exactly the advice students should follow. If a student goes to Harvard, but does not mesh with their graduate advisor, they will come out ill-prepared, if they finish at all. At the end of the day it's the same for scuba training. I always tell prospective dive students to ask around for feedback on instructors in their area, go and talk with the instructor and decide if they are someone you want to work with.