I highly recommend staying at Eugenie's place. The location is excellent (close to everywhere, e.g., the metro, Le Bon Marche, restaurants, and other visiting places in Saint Germain), the apartment is very secure and clean, the room is beautifully decorated, and everything is well-equipped. Most of everything, Eugenie is a wonderful host - we were staying over the holidays, and Eugenie was on messages on Christmas and new year's day.
Tips: (1) Follow her instructions if you're coming early and checking in without her because the apartment units do not have number signs. Eugenie's instruction is exact. (2) Also, it's great for a longer stay that Eugenie sends her cleaning person every Wednesday (1-3 pm-ish). (3) there's a 24-hour on-site doorman, and the entire apartment is gated. Very safe and secure!