Natives vs. Non-natives

I think we already had this debate in both classes I am taking. Who is a better teacher -a native speaker or a non-native speaker? Interests and opinions clash. My answer is - a professional. If a person is a proficient English speaker, studied to be a teacher, and has a degree in TESL or a certificate such as CELTA or DELTA it does not matter what their first language is. Personally, I think that THE best teacher is a non-native with native-like fluency, experience of living in an English-speaking country and desired credentials. The only real advantage I see for the native speakers is the knowledge of slang/idioms, but that is easily corrected.

I found that students like it, when the teacher is a non-native speaker, because then you get the hardly refutable argument of "hey, I was able to learn that, so you should be too". It is also nice to share stories of your first mistakes, because then they feel that a) their mistakes aren't unique, b) making mistakes does not mean you won't be able to master the language. Finally, students feel sort of companionship with the teacher and know that the teacher is able to relate to their problems. An average native speaker hardly has an idea of what a mess English prepositions are :)