The curricula for most open water classes are very similar. What is different is how the classes that present those materials are structured. A class can be built around the minimum time required to do the minimum required instruction, or it can be spread over more time, with more opportunity to repeat skills and work on things which have proven difficult. Often, how the class is presented is more dependent on the philosophy and economics of the dive shop and/or the instructor, than which agency's logo is on the card.
In addition, something which often isn't considered in choosing a class is the ratio of staff to students. Even if you only have one instructor, if you have a number of assistant instructors and divemasters also working with the students, the student experience can be superior to that of a student in a smaller class, but with no certified assistants involved.