Alfonso's place was a great pick for me. I was stopping by Madrid to see friends and put things into storage, so it was a convenient central location. I think it's particularly great for tourists since it's close to Plaza Mayor and Sol. The only downsides were that it's a walk up to the third floor (but this is common in Madrid) and the hot water often ran out so I had to take quick showers. Otherwise, it's a cozy place that's good for one or two people.