What is the best job in teaching English as a foreign language?

That very much depends on personal taste. In terms of the most rewarding, probably just a regular old class teacher. In terms of the highest status and skills, then perhaps Director of Studies. In terms of flexibility, perhaps online English teaching as you schedule your classes around your life and are not tied down geographically. The best job in TEFL is really a misnomer – what do you value most highly is the best way of finding an answer.