Montmarte is probably one of the very best places to stay in Paris - if you do stay there then I really recommend doing the Sandeman's walking tour. You'll find out where all the famous artists lived and you'll see unforgettable sights that most tourists sadly miss.
Also pop to Coquelicot (24 rue des Abbesses) for breakfast - this café consistently wins awards for the best bread in Paris and locals queue for the baked goods because the quality is so excellent. The bowls of hot chocolate are worth waiting for too!
Hope you have an amazing holiday!