Juan-Carlos is by far the best host I ever had.
Previous to my arrival, he wrote several time, making sure I know how to get to the flat, sending my maps and all. The room is great, quiet and not that hot for a summer in Madrid! Juan-Carlos is respectful, let you have privacy but is also very knowledgeable about Madrid. On my first night, I joined him for a walk and he showed me lots of streets of Madrid so that I would know the city better.
I highly recommend Juan-Carlos!