Well, anyone who knows me already knows my choice.
Of course people mention Moneypenny, and she was 'M's personal secretary, but anyone who hasn't read the books doesn't know that the '00' section had their own secretary, Loelia Ponsonby. She was secretary to 007, 008 and 0011, and they all tried and were all rebuffed by her. Gotta love a woman who can say no to James Bond and friends.