It is near impossible to say anyone is the best director of all time but i can say that Martin Scorsese is the most Consistently great. If i were to list all the great movies he has made I would have to list almost all of them, and it is defiantly debatable that listing all of them would be justified. From Mean Streets to Hugo, Scorsese has proven to be a master of cinema and the greatest story teller of our time. Anyone who loves film loves Scorsese.
Just watch this
The most successful director of all time not just a incredible director but a outstanding business man. The only bad thing that he ever made was unintentional, that was a Hollywood based around franchises and merchandising. Without him we would not have the Hollywood we know today whether you view that as a good thing or a bad thing you can not blame him for making movies that were successful.
There is no doubt James Cameron is a incredible director his ability to innovate and to capture the essence of imagination is unmatched, but personally i feel he is just not a great writer and that's why his movies like avatar are criticized an way he is overlooked as the amazing director he is because the poor writing drags the quality of the movies down, but he truly is one of the top ten directors alive, but just an okay writer.
Christopher Nolan is the most promising new director of the 21st century. He personally Turened a dead Franchise into possibly the greatest superhero series of all time. he saw promise in Heath Ledger who's only other major roll was Brokeback Mountain and then he drew out a Oscar winning performance. in memento he blew minds, in dark knight he put them back together,in incepetion he completely destroyed them .only time will tell what will come of this promising director but my guess is in ten years he will be universally considered one of the greatest directors of all time.
Peter Jackson sprung out of nowhere to director of probably one of the best fantasy movies of alltime and one of the best adaptations of a book since the godfather. he would be hire on the list if not for the fact that i haven't seen the effort and skill he put into The Lord Of The Rings since the last in the trilogy.
I personally liked but did not love The Social Network but i did fall in love with The Curious Case of Benjamin Button and Fight Club making David Fincher a nesascity for this list. He has very distinctive way of directing and even though he has made very diffrent kinds of movies you can always tell its a David Fincher movie.