I cannot say enough good things about Sonia and Miguel and their place. Miguel offered to give us a ride from Lisbon to Sintra, as he was driving from the city and we were close to where he works in Lisbon. This was beyond helpful, as we were traveling with our 3.5 month old. Throughout the entire airbnb process, Miguel and Sonia kept in great contact and sent a ton of helpful information before we even got there. Miguel also spend a nice amount of time going over things to do and his suggestions once we arrived at the apartment.
The apartment itself is in the absolute best location - right in the historic center of the city. This made getting around so easy. The only very slight bad part, and this is only if you want to go to bed before 10pm, there is lovely live music outside the window at the restaurant below (which was delicious). The music did not bother us or our baby at all though. Oh, and the apartment is baby/family friendly, which was a huge huge plus!
If you are looking for a place to stay in Sintra, do not hesitate to book with Miguel and Sonia.