All wrong on David Niven, I'm afraid - the first big-screen Bond movie was Doctor No in 1962, Niven's Casino Royale was actually 1967, after all of the Connery Bond movies.
See
this wikipedia page for the full story. It's complicated...
I voted for Connery but it's a difficult choice - nearly all of them (even Lazenby) have their good points, Roger Moore is the weakest but even he had occasional good moments.
