If you are only in Paris for a short trip and want to make the most of your time (and if your budget will allow) consider staying in the St. Germain neighborhood. You will be right next to Notre Dame, Musee D'Orsay, and the Pont Neuf bridge, plus you will be close to the Luxembourg Gardens and many metro stops. This is really the center of Paris. It's home to the famous Les Deux Magots cafe and has a long list of famous inhabitants including Ernest Hemingway and Albert Camus. Get a room with a view of the Seine!