My students here at CBNU often ask me what I think the best “kind” of English is.  They want to know whether British English is superior to American English, or vice versa. There can only be one answer to their query: American, British, and many other varieties of English are considered legitimate and viable means of international communication; thus all are worthy of careful study.
  Textbooks published in Korea often favor approaches to standard grammar that are British, but idioms and spelling rules that are American.  Public and private school directors tend to prefer the American accent, yet they hire (with the blessing of the national government) native speaking teachers from all of the "inner circle" countries (England, Australia, Canada, New Zealand, the United States, etc). What all of this means is that the average Korean college student has already been exposed to a great mix of World "Englishes". 
It is also important to note that most of the major internationally respected English proficiency tests now include lectures and discussions conducted by speakers from many different countries. Making the effort to study varieties of English can therefore have the very practical effect of improving your scores on such tests.
  Finally, knowledge of these regional variations is valuable because one day you may actually work and speak with people who have different backgrounds in English. It is easy to imagine the ways in which British, Canadian and Australian colleagues and clients will speak differently from each other. What about future co-workers with whom you will communicate in English, but who are second language learners just like you?  A Spanish speaker who learned English in South America will probably sound more American.  Someone from Hong Kong or Malaysia will probably use more British structures and idioms. Developing some international elasticity in your English ability will help you communicate better with all.