Concise Oxford English Dictionary
The COD has always been the best small English dictionary. Its rivals have drawbacks: Chambers has too many obscure Scottish words, and Collins lacks many useful words.
The latest edition of the COD updates the vocabulary well, without including too many temporarily topical words whose life is likely to be short.
My only criticism of the latest edition is the inclusion in the middle of a guidance section. This should have been at the beginning or the end. But this is a very small point - perhaps largely a matter of taste - about what is otherwise a very useful book.