I highly recommend Jose's apartment in Madrid. It is perfectly located and very spacious, and Jose is a wonderful host.
For people who plan to really explore Madrid, the location can't be beat. The apartment is right off the Plaza de Oriente, meaning you're anywhere from 5 to maaaybe 30 minutes on foot from the major sights (including the Mercado de San Miguel, Puerta del Sol, and Calle Cava Baja), close to great metro stations, and a nice walk to Moncloa (in case you want to take a day trip!). Leaving each day and walking into the beautiful plaza or onto the Calle Bailen is amazing. The location alone is worth it.
Also, the apartment itself is very spacious. I was on a trip with four people all together, and we could easily have had more people with us. The rooms are nicely sized and far away from each other, plus each has its own bathroom. The living room is very large and a perfect place for everyone to gather, with huge windows. We had a glass of wine in there almost every day. The only thing about the apartment that wasn't perfect was that the place is so large that wifi isn't strong everywhere -- the bedroom farthest from the living room doesn't have a great signal, so just keep that in mind and strategize about who should get that room!
Finally, Jose is a great host. I emailed and texted him with a lot of questions before we got there, and a few while we were there too -- he was prompt and nice each time. I have zero doubt I would stay at Jose's apartment again, if I had the opportunity.