Which English dictionary apps would you recommend??

As an English learner and English is my second language, which English dictionary mobile apps (For iPhone) would you recommend. There are a lot of brands Oxford..Macmillian........etc in the market. I don't mind paying for a good dictionary but I don't know which one to choose. I hope that it comes with clear examples on how to use the word I don't know and does not give too many explanations or meanings on uncommon use. Sometimes some dictionaries like to put a lot of rare words or usage but this makes it difficult to learn practically, at least for me. Thanks a lot.