I recommend Antonio's place. The place was very clean and quiet, has a well furnished kitchen including coffee, good elevator, good bed and storage, and nicely decorated. Location is great, near Sol Metro stop but a bit closer to the Opera Metro stop. It look 40 minutes to get to the airport with only one transfer (Renfe C3 or C4 train (platform 1) from Sol to Nuevos Ministerios, then transfer to Metro 8 Aeropuerto T4 which stops at all terminals).