teacher should be man or women?  

A teacher should be someone who is knowledgeable and interested in the betterment of the students. Gender of the teacher is irrelevant.

Doesn't really matter, I think a man or a woman could be a teacher.

It doesn't really matter. I've met a lot of women who should have chosen some other profession as they were horrible teachers. And I've known some men teachers who were gorgeous in teaching and in communicating with their students.