The dominant instructional model(s) of the course should be selected according to the goal of the curriculum and the needs of students, and the varieties of English represented in the teaching materials should match the focus of the course.
In many cases, American or British English – the two most popular choices for instructional models – may be a reasonable choice. They are considered legitimate and respected in many international contexts – i.e., they may not be the most preferred in all contexts but are acceptable in many. After all, there is nothing wrong per se with these varieties.
Aya Matsuda in Lubna Alsagoff, et. al (2002: p. 173)