Rescue and the Master scuba diver *class* (e.g. via NAUI) or an intro to tech (in single tank gear) might be a good choice. You should learn a lot. People will understand the intro to tech, though they may not understand the (NAUI) master diver. Oh well. In all cases, the card just puts you in provisional OW, AOW, post AOW, and maybe really Ok bins. Talking, gearing up, and in water will tell more of the truth.
Unless you want to start teaching, I would not yet do a leadership class. Yes, you will learn a lot, but you also gain legal liability as you are then a professional who may have a duty to have performed in some manner. And you might feel the need for yearly insurance to guard against that liability.
In NAUI, all the leadership level physics, physiology, etc, are tested in the non leadership NAUI master diver class. So NAUI Dive Master needs NAUI Master Diver (or equivalent).
For the side discussion:
That equivalency requires at least passing the master diver exam, though you do not need to become a NAUI master diver. I'm currently a NAUI Dive Master candidate, I've passed the NAUI Master Diver exam, but I am not a NAUI Master Diver. And as of recently, leadership grades start with a FIT class that then branches out to the others, like Assistant Instructor and Dive Master.
Edit:
Mephki, It seems you may be asking where to get such dive training. It would help to let people know where you are based, or what warm water you have in mind, like Florida, the Caribbean, etc.
