What Language Should We Be Using In Our Classrooms?

With the growing English education fever in Japan in mind, it is high time to consider what would be the ideal in-classroom-language for teachers to use in daily English lessons. There is a debate about whether native English-speaking teachers (NEST) or non-native English-speaking teachers (NNET) are best for in-class instruction, as well as the use of L1.
This discussion and workshop will talk about this issue, and others, from the perspective of the presenter, who studied Akita high school students and how they reacted to English and Japanese usage in the classroom. It seems that students prefer using L1 and L2 depending on the purpose. What do you think? You thoughts, opinions, stories are welcome with open arms.