Hi... depending who you are dealing with... really!

i think you mean which one is most used , or which one is more useful when working with foreign for example?

none

An accent is an accent. I can't see why one is 'more useful' then another. OK, if you are a actor you may not get roles based on your accent. Or if you have a very strong accent (Arnold Schwarzenegger) you may get only non speaking roles (Conan), or some with very few lines (Terminator). But the pay was still ok.

Hi, it depends on what is accepted the most in your country. There is no single accent which is most important or useful.