We highly recommend Madeleine's place. And Madeline is a charming, extremely helpful and responsive host. Don't hesitate!
The location on rue des Martyrs cannot be beaten, with world-class boulangeries and restaurants and food shops right on the doorstep. There are 4 separate metro stops in easy walking distance (for lines 2, 12 and 7) - it took me 20 mins from leaving the apartment to walking into the Musée d'Orsay for example - and you can walk down to Opéra and Galleries Lafayette just as easily as you can walk up to Montmartre and Sacré Coeur.
The apartment itself is excellent: there are parquet floors and high ceilings and large windows (with a lovely view down the street); it's perfectly quiet; and it's clean and tidy with a good working kitchen and nicely sized bathroom. In short, it has everything you'll need for a stay in Paris.