We had a really good stay at David and Ana's place. The flat is situated in a very nice nighboorhood. It's in walking distance to Madrid's center. The area is full of nice little bars for getting some tapas and a drink.
The apartement was very clean. It's beautiful decorated and it has everything you could possibly need. And David and Ana are very helpful hosts. They will give you some great advices for some non-touristic things to see in Madrid!!!