Which English dictionary should I buy?
Oxford Advanced Learner's Dictionary, 9th Edition
Longman Dictionary of Contemporary English, 6th Edition
Collins COBUILD Advanced Learner's English Dictionary, 9th Edition
Cambridge Advanced Learner's Dictionary, 4th Edition
Macmillan English Dictionary for Advanced Learners, 2nd Edition
Merriam Webster's Advanced Learner's English Dictionary, 2nd edition
Could anyone tell me the difference between these dictionaries? And which one is more useful than the others in IELTS exam? Thank you in advanced