First, you should know that Los Amigos is a backpacker youth-hostel-like place, complete with bunk beds and group restrooms/showers. I understand it is cheap, but very public. And I'm not exactly sure why, but according to my sources in city government, they're not yet listed as an official accredited/licensed lodging establishment in Madrid.
If you use the SEARCH link above/right, you'll find feedback about Hostal Villar, Gonzalo, and maybe Aguilar. I don't recall seeing anything posted on any of the others, but do use the SEARCH link to check your list of hostels (called "hostales" in Spanish) and my memory.
I usually trust Let'sGo guides, but know that those recommendations were recommended by one or two writers. You would do well to take seriously the feedback/recommendations of the posting on Madrid's and Spain's hostels here in this forum. Afterall, the people here are REAL travelers, people like you and me.
Have a wonderful time in Spain!! I know you will.
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