The Penguin English Library Adventures of the Engineer's Thumb and Other Cases

As usual with the Sherlock Holmes stories it is very hard to say which are the best - but there are many stories here which would get the vote - ranging from The Boscombe Valley Mystery to the wonderful Adventure of Silver Blaze, from the Adventure of the Norwood Builder to A Case of Identity, but above to the uniquely strange and macabre Adventure of the Engineer's Thumb.