There are a number of scuba and related organizations around the world. Most of them have high standards and provide comprehensive diver training. Is there enough difference that it really matters which on you are certified through?
The agencies around the world pretty much meet the same basic standard for open water scuba instruction. Open water courses include a syllabus of diving theory (physics, physiology, and so on) along with practical skills. Classroom or homework supports the student whether a rookie or experienced diver who is looking for more.
Some agencies allow leave the number of lecture hours and pool sessions at the instructor’s discretion. Also, it is not uncommon to see some instructors exceed an agency’s minimum standards. In my humble opinion being restricted to teach just the minimum, no more, no less especially when the instructor is a seasons diver is cutting short the exposure one may experience.
Regardless of which …