I will probably bring the wrath of the moderator gods down on myself for this reply and may scrape some limestone off rules 4 and 6 but this one hit a nerve with me so here goes. Get your basic and advanced openwater certification from one of the scuba training agencies. But, when you start talking about nitrox, cavern, cave, trimix go with one of the leading agencies such as TDI, IANTD, NSS-CDS, and NACD. These organizations were leaders in these disciplines long before any of the basic scuba agencies were. It is obvious that the basic scuba organizations got into this later attempting to take market share as these disciplines became more and more popular. BUT, if you are going to spend your money in the adavanced disciplines, at least get certifications that are from organizations that are on the leading edge. My occupation is that of a commercial diver. I went to commercial diving school many years ago to be trained by commercial diving educators in cold, black, muddy water and I now use helmet gear designed for working divers. When I decided to take cavern, I went to Florida to be trained by cave divers. I modified my equipment and dive practices in order to dive in overhead and now use the technique for ALL my sport scuba activities. I went into three different "holes" in the course of two days. It made me a better and more comfortable diver and I will be eternally grateful. If I have time to get into cave, I will return to Florida for my training. I recently had a friend, who has only been diving a couple of years, to tell me that she had just received her cavern certification from one of the basic scuba organizations while training at a North Carolina coastal town. This was against my advice based on my 30+ years of diving. I asked her how many caverns she visited (since we have so many here in North Carolina, NOT). So, if you wanna be, you gotta go where they do, and you gotta train with those who are. Enough said.