Most non-native speakers are trained teachers either in their country or the country they teach in which means that they often will have much more teaching experience than native speakers. It seems foolish to assume that just because someone speaks English they can teach it effectively. Without training in classroom management and lessons in English grammar, native speakers cannot be effective ESL instructors. They may be able to speak the language but explaining it is an entirely different matter. If a native speaker is a qualified educator, then they will have an advantage but when teaching abroad, as mentioned above, it is also beneficial to be able to communicate with students in their native language. When native English speakers are paired with local teachers, students have the best of both worlds.

I think the teacher, for whom your language is native

From my own experience the best teacher is someone, who is more than bilingual and familiar with challenges of learning second or third language at first hand.  I`ve been learning English for three years with four native speaker.  The best of them knew three and more languages.

Native Speaker.