Hotel Avenida is a good place if you're traveling on a budget. The location is excellent. 15 minute walks to many sights, and 2-3 minute walks to a few different metro stations, and tons of restaurants and stores nearby. I recommend the pastry shop next to the hotel, as I stopped in every morning for a croissant or tortel chocolate before heading out to explore Madrid.
While the hotel is showing signs of wear, it is clean. The rooms are small (which is typical of European hotels), but bathrooms are a good size. They provide large towels and hand towels, but no wash clothes, so bring your own. This is also typical of European hotels. Also, other than body soap in a dispenser, there are no extra room amenities like lotion, coffee pots, or refrigerators. There is a small safe in the wardrobe. The beds are very firm, so if that's not how you like your bed, you may not find them comfortable.
The staff is wonderful. Most speak at least a little English, and are friendly. They provided recommendations for sights, maps, and arranged for a taxi to the airport. Overall, the hotel was perfect for my needs while my niece and I visited Madrid for 9 days.