That depends a lot on what aspects of the 20th century Middle East you're interested in but the two books I cite and recommend most often in this sub as being the best and most concise for 20th century political history are Eugene Rogan's The Arabs: A History and D.K. Fieldhouse's Western Imperialism in the Middle East 1914-1958

Malcolm Yapp's dual volume The Making of the Modern Near East, 1792-1923 and The Near East Since the First World War would be a close third, but I think Rogan's is better and more readable as a single-volume text.

Having read more about Iran than the rest of the Middle East, I would recommend Michael Axworthy's work. Empire of the Mind covers a lot more than just the 20th century, but it wouldn't be a problem to only read the later parts, and the follow up Revolutionary Iran is also a wonderful read.