We had a great time at Montse's apartment. It is nicely decorated, fairly quiet and well located (within walking distance to the Sagrada Familia, and with two metro station nearby). Plenty of room for the five of us for one week. Montse was very helpful with our planning of visits, and easy to get in touch with during the week.
Note that there is a guarded car park nearby - around 60€ for a week, not cheap but worth it since a car is of not much use in Barcelona, and parking not easy in the vicinity.