We chose Ares's place mainly because of its proximity to Caja Magica, as it is about 10 min walk, very convenient for those willing to attend any events taking place there. Although the place is a bit further from the city center, reaching it is very quick and convenient, there is a tube station nearby (the tube goes straight to the Sol square every 4 minutes). There are also a couple supermarkets and several places to eat just around the corner.
As for the place itself, it was very clean and comfy, the breakfast was nice, and, most importantly, the host was very hospitable and friendly (aaand spoke English very well, which is not that common in Spain from my short experience :) all in all, our stay in Madrid was an extremely pleasant experience, and Ares's place had an important role in the overall goodness of it. I would definitely recommend it, obviously :)
Good luck!