If you're going to Madrid, then you have to stay at Julia's place. It's location is very convenient, located in the city's center with 2 metro stations and the famous Plaza Del Sol within a 5 minute walk.
Additionally, Julia was absolutely wonderful. It was like staying with family for the 2 days she was there. Anything we needed, Julia either already had it prepared or was very accommodating. We even had a slight misunderstanding and she rushed home immediately to take care of it!
Great location, great owner, Highly recommended.
It's also highly recommended to have a basic to intermediate knowledge of Spanish as Julia doesn't speak too much English.