This a question that does not have a single answer. This is because a "best teacher" for one particular person will not be a "best teacher for a different person. Each teacher has strong points and these strong points are different with different teachers. One teacher is very good with grammar and another is good with accent reduction, while yet another will be excellent with improving conversational skills.Each student has different goals so the student should know what she or he needs and then judge who is "best" for this student. Of course there is the question of competency. Teachers vary as to how well they can teach. That is another issue.

Me.

It is me lol