What is the best Ex system for me?

We have received too many times this simple question from customers all over the world. Few remarks here:
– Ex as a legal system shall not be chosen by company, but it shall come from country’s legislation
– if this does not work, company shall come to decision. And this decision shall be followed in all cases
Note: it does not work, that for one application I choose the most applicable one, and I do choose sg different for the next one.
Keep up good work!
Eg.: ATEX, IECEX…