100% recommend Montse’s place. Location is amazing, a quick 10minute walk to Sagrada Familia, and within walking distance of 3 tubes stations (Monumental, Encants and Glories). Any of these will take you to any other place in the city in less than 20 minutes. If you’re a walker, you are roughly 30 minutes way (walking) from other landmarks. I highly recommend doing that as you’ll discover much more than by public transport. 5 minute walk to two big supermarkets and breakfast spots.
House wise: super clean and comfortable, we had everything we needed, we didn’t have any problems whatsoever and we felt quite at home! For us 5, it was the perfect size but you can easily fit a 6th person without compromising overall comfort. The building is quiet and tidy with friendly neighbours. Montse was very welcoming and quick with her replies, and her son was spot on with some local tips! :)