Jesús made me feel very welcome at his place. He met me by the metro station and explained how everything worked in the apartment, anticipating any need I might have.
The apartment is spacious and in a quiet green neighborhood of Central Madrid, close to one of the main train stations (10 mins walk) and several metro stations. The room I was staying in is a good size, with a super comfortable bed. My favourite place was the kitchen though - it's a sunny terrace with a view over a green yard, I enjoyed having breakfasts here every morning.
Considering all the factors - location, size, the facilities, host's friendlessness and the price he charges, this option is strongly recommended.