WW2 best spy

Peter Cheyney (b. 1886)

All his spy novels - Cheyney wrote many other novels, notably with the FBI agent Lemmy Caution - have "Dark" in the title and are commonly known as the "Dark series". Cheyney, contrary to Fleming, is always believable: the atmosphere is always right; There is violence in these novels, but not the sadism, sex and sexism that end up being so annoying in more modern novels. And of course all this Dark series is about fighting against Nazi agents. 
Dark Duet This is a counter-espionage novel. Mrs Marques is the unforgettable Nazi spy at the center of the action. Part of the story is set in Portugal, and the signal for the bad guys is a conga dance.
The Stars are Dark Double agent against double agent.
The Dark Street The story starts in Paris. One of the best of the series.
Sinister Errand Agents of both sides do not know whom they can trust. They dance around each other vaguely menacing each other. Not a very exciting book.
Dark Hero
Story of a Chicago mobster who becomes a war hero in Norway. He is betrayed by the woman he loves, ends up in a German concentration camp and dreams of revenge. Impressive book!
Dark Interlude*** Agent O'Mara plays a drunk, unemployed ex-agent, and for the sake of his role, drinks too much.
I do not remember Dark Wanton and Dark Bahama.
Eric Ambler (b. 1909)
Ambler was a pioneer in the genre of the accidental spy. You might give a try to Epitaph for a Spy. The action is in France before WWII. It is a classic, closer to Agatha Christie than to the modern spy novels, but it has charm.

R.V. Jones (b. 1911)
Of all the real spies who wrote their memoirs, Jones stands out as a real genius. He was during WWII the British chief of scientific intelligence and incredibly successful. He was a delight to read and a delight to meet with. His main book comes under two titles (one UK and one US) : The Wizard War or Most Secret War***
Adam Hall (b. 1920)
The Quiller memorandum*** made a vital impression on me in the sixties when it came out. I was young, I believed that fascism was a thing of the past. I had not realized that the danger is always with us, as evidenced by genocides and dictatorships and racism, and anti-immigrant policies unrelated to good management that plagued the last fifty years, plus a lot of scary events, such as the French fascists being the third major party in France. The Quiller memorandum opened my eyes to reality which is why it is an essential book for me.
Len Deighton (b. 1929)
Deighton is still a delight to read. Try Berlin Game, Mexico set and London match.
Aaron Elkins (b. 1935)
Elkins is mainly known for delightful archeological "bones" mysteries, but he wrote a remarkable book about the art treasures stolen by the Nazis. The book is called Loot and takes place around 1995.
Frederick Forsyth (b. 1938)
Forsyth was an investigative journalist and has a knack to understand and describe methods that can be used by the bad guys. It is said that Bob Denard, who captured the Comoros islands had a copy of Dogs of war to inspire him. Forsyth once had a project to write a novel about terrorists hijacking a plane and using it as a weapon. He thought the idea might be used by bad guys and did not write the book (this was several years before 9/11). All his books are well documented and fascinating. In The Odessa File, the story of an organization protecting Nazis after WWII, you will meet real people such as Edward Roschmann (real-life Nazi assassin) and Simon Wiesenthal (real-life Nazi hunter).
Alan Furst (b. 1941)
A well documented American author. Dark Star (1991) is full of spies and if you are interested in the relationship between Hitler and Stalin, the book comes with a point of view. This excellent author cannot always be trusted. His history of the German invasion of France is not accurate (so you could avoid The spies of Warsaw, 2008) Many readers complain that the last books are not as good as the first ones. So, check the date! I only read these two, so I would not know for sure.
Philip Kerr (b. 1956)
Like many authors writing about historical periods, Kerr can make some factual mistakes, but you certainly do not feel them: the atmosphere is always right. His book March Violets, situated in 1936 Berlin, and the 2 next books which form the trilogy Berlin noir are extremely strong.