for me the answer is take what classes you need to do the diving that you need to do. This only applies if the training is done properly, i.e. most PADI OW divers are woefully inadequate for normal diving conditions and PADI tends to substitute good depth in each of their courses with volume of courses. This goes back to the quip about their equipment specialist and peak buoyancy control classes. They remove time spent on those two very important aspects of diving in their basic OW class and encourage them to take those classes down the road, i.e. Put Another Dime In.
IF the training of OW diver is done properly, which unfortunately pretty much limits itself to university courses these days due to timing constraints, most divers don't actually need anything beyond that. I think Nitrox should be included in every OW class from day 1. It's negligibly more math, and the last two dives at least with NAUI can be dove using Nitrox. At NC State each diver gets NAUI Nitrox Diver as their cert, they have buoyancy control that rivals most instructors unfortunately and can do things most AOW divers can't. Proper training.
Some then decide that they want to further their training to get into technical diving or professional, so they have to take Rescue, that's required for damn near every cert out there. In their OW class they learn how to do proper unconscious diver at the bottom rescues, and the main rescue tows with rescue breathing etc, so they're prepared for an emergency, but Rescue gets you BLS certified at least with us, so you can do surface treatment once they're out of the water.
After that, the only real course they have to take is a decompression course if they want to start diving the deeper wrecks off the coast of NC, and everything else they need to learn is best done through experience and diving with mentors. We have a very good group of mentors, most of whom are technical divers, some of them very well renowned in the industry. Nat Geo videographers, Rolex Diver of the Year, etc etc, and these guys dive with new students regularly, that's more valuable than any course they could take because it is continued education on a regular basis. Every time they dive with these guys is almost like taking a class in the school of hard knocks because we critique everything and they usually get video feedback of it and then over pizza and beer we can discuss what happened and how to make it better. You don't get that in most classes because of ratios and instructors being paid etc etc.
For me this holds true, get the certs that you need to do the dives you want to do. I don't want to be told I can't go on a dive because I don't have a c-card in my hand, I want to tell myself I shouldn't go on that dive because I'm not prepared. Current cards, Nitrox Diver, Rescue, AI, Full Cave. That's it, and that's all I have needed, I blend my own trimix if I need it for specific dives, but I'm not paying for the cert until I'm on a rebreather because of the cost of helium. When I went for cave training I didn't have to have dive fundamentals taught to me because they were taught from day 1, so all my instructor had to do was basically go diving with me so through experience I could figure out how to navigate inside of the caves, that's the way it used to be way back when, but unfortunately that has been lost.
That's my thoughts on it at least, obviously this only works in a very finite group of divers, but unfortunately I think that the sport has progressed passed the point of no return on universally providing true quality education to the masses, and outside of GUE/UTD and the universities, no instructor is really able to devote the proper amount of time to students prior to getting certified. Doesn't matter how good of an instructor you are, students can only learn the skills needed through hours, not number of dives, just hours. This is only made worse by the current requirement for instant gratification on everything so the thought of spending more than a long weekend to get scuba certified is deemed not worth it by most.
