NAUI was first. There were two NAUI-certified guys (one of whom my instructor knows personally) who thought NAUI should relax their standards to make diving more accessible to the public. When NAUI say "nope", they went and formed PADI.
Today, NAUI is non profit and continues to be the agency that certifies and teaches the US Military, including Navy SEALS. PADI is a for-profit organization that spends a lot of money in marketing.[/quote:

From my own experience, I can say that what he said makes total sense. The PADI course I started in Jamaica a few years ago pales in comparison to the NAUI certification I’m now working on, both in thoroughness and depth (pun intended). Right now, I’m at the same point in my NAUI courses that I left off in the PADI course, and I perceive a real difference. I already feel more competent and self-sufficient, though I know I still have a long way to go (100 dives according to this instructor) before I should consider myself a fully safe and competent diver. I found the attitude of my PADI course to be a bit more cavalier, which I personally didn’t like. Surely the instructor has a lot to do with that, but such was my own personal experience.