Divemaster / Instructor Certifications - Max "coverage" for fewest agencies

[Offshore]

First of all, I want to ask that this please not turn into another "X agency is better than Y agency" thread (read many of those already), or another with several "the instructor/trainer/shop matters far more than the agency" answers (I definitely agree with that, though).

As a student, I was fortunate enough to be able to try out several different training classes with several different agencies (PADI, NAUI, SSI, NSS-CDS, and IANTD), partly because instructors I wanted to train with happened to fall under all those different agencies, but also because I wanted to see what differences there were in things like standards, quality of books, etc. Fortunately, unlike in sailing (where I've had to pay fees and take cross-over tests as a STUDENT to go from ASA to US Sailing), all my cards from all the different agencies crossed over and were recognized as each others' prerequisites with no problem at all. Now that I'm considering taking the step towards Divemaster and Open Water Instructor, it seems that unfortunately I have to make a commitment to follow the track of one agency, and deal with cross-overs and additional instructor training to be an instructor for more than one agency (which in some cases makes perfect sense, since I don't think NSS-CDS teaches open water nor do I think PADI teaches Advanced Nitrox and Deco procedures).

So far, I've heard very little reason not to do the PADI route because of their dominant global presence. Given a few of my casual objectives (be a cavern guide, be able to introduce friends / acquaintances to diving and accompany uncertified first-timers, teach nitrox / cavern / ice / wreck, etc. specialties), it seems that "no card is more accepted" (except in some places, CMAS), and enough people will see PADI signs at resorts and look on websites for PADI instructors wherever I may be that I shouldn't worry about finding opportunities as a PADI professional. So for now, I have NO reason to believe that getting the PADI certs would be a waste of time.

What I've had a hard time shopping for is OBJECTIVE differences between the agencies as far as how they serve / back up their divemasters and instructors who choose to follow their respective paths. Some questions:

1. I've once seen a pie chart of how many divers get certified by which agency, and saw that clearly PADI was dominant with NAUI I believe as a distant second. I can't find this pie chart any more, but would also love to see it broken down further (by geography, by how many advanced students stay with PADI vs. doing specialties elsewhere like me, etc.)

2. Are there large regions where other agencies are clearly dominant? I currently live in the US Northeast, but would also be looking at Central / South America, South Asia, and East Asia. PADI has been dominant everywhere I've been except for Northern Florida Cave country and in technical circles. I have seen online that CMAS seems to be dominant in places like France and Iran, while BSAC seems to have huge presence in the UK and Japan.

3. What are the objective costs (both financial, commitment-wise, re-certification), etc. involved with one agency vs. another? I've heard some say their annual cost of being a PADI instructor is much more than their annual NAUI cost, etc. I've also heard that one agency requires cave instructors to do a rigorous re-certification each year.

4. Which ones are most difficult /expensive to cross-over into?

5. If I did go PADI DM / OWI, which second agenc(ies) might most expand my coverage (geographic or in terms of what I could teach) with a minimal amount of overlap? (For example, I've thought of PADI and IANTD, but NAUI seems to have a better integrated OW - tech overall package).

Thanks in advance for all the (hopeful) information!

[Hawaii Scuba Divers]

I am PDIC Instructor Trainer and took the IANTD Instructor Course including Rebreathers and I think that for TECH side is Good Agency and Materials are online..
You are just looking to work around the country then you are right put another dollar In is biggest kind of like MIKEY D'S...
Aloha Mark.

[marinediva]

Gaining your PADI Instructor cert first is far more economical.
It is cheaper to do a crossover from PADI to another agency then the other way round.
PADI require you to do an IE.
sucks.
As far as I know they are the only ones. They do not recognise the other agencies.

I am a PADI instructor who is planning to do a cross over to BSAC.

I am studied their courses and they are truly amazing.

[Dive-aholic]

If you're planning on working overseas (specifically the places you name), then PADI is your best option. It is also easier to crossover to some other agencies as a PADI instructor than it is to crossover to PADI. If you plan on teaching for a shop, then PADI is also the way to go. If you plan on teaching independently, then there are better choices out there through agencies that support independents much more than PADI does.