Go to Carmelo's house. The place is central, very clean, with personal decoration and cute thoughts (like earplugs for light sleepers) . The host is nice and ready to answer any of your questions. The bookshelves are also full of tips to visit Madrid and Spain in general, in several languages, so even if it is your first time in the capital, you will know where to go. Check-in was fast and easy, as was check-out. I would recommend this place to everyone.