We had a very nice stay at Alvaro's place. He's perhaps the most responsive Airbnb host I've ever had—he answers messages within minutes. The location is really convenient: we walked everywhere and never took public transportation. If you don't have a lot of luggage and don't mind a 20-minute walk to the Atocha station, you can even take a direct bus to and from the airport. The apartment is very clean and quiet (we didn't hear any noise from the neighbors).