Native speakers are certainly preferable if I have learned the language to some level and want to make it better. I want to know how do they really speak. If I take a lesson of the person for whom my own language is native how do i know that she does not teach me some artificial language of English Department of some Russian university? Some cliche and even errors of native speakers are much better than artificial fully correct language of foreigners.

For me, I think native speakers are better. Their manner of speaking and behaving gives more motivation.

Phonetic is one of the reasons I specially choose a native-speaking teacher of any language, in this case a native english speaker after that I choose someone for her / his background, however, if I find a non-native speaker with a good fonetic / pronunciation and background, I would choose her / him undoubtedly

I don't care at all if a teacher speaks my language because I want to practice the target language and not speak in my mother tongue. I don't even care if the teacher can speak English well as English isn't a target language of mine either and I don't want to spend the precious course time with chatting in English but only the target language. A good teacher doesn't need a second language as a crutch to teach a target language.

Normally, I'd choose a proficient native speaker of my target language and a proficient non-native speaker is my second choice. A native speaker who is not proficient in my target language isn't of much use for me as my goal is not to sound like an ineducated speaker of a language who only knows street talk but eventually I'd like to be proficient as well and sound like an educated speaker of that language.

I am studying with both teachers: native speaker and the teacher for whom my native language is native as well