Usually I take the
Marriott Auditorium Madrid Airport if I want to stay just one night at the Airport. It has a very nice and huge Exceutive Lounge that allows you to enjoy some privacy in this huge Hotel. Rooms are refurbished bathrooms are very good for spanish standards. Howevery you can still feel that it has been a different brand before. They have as well a shuttle service to the airport. However you have almost nothing around. So I can`t recommend it if you are looking for some evening tappas in walking distance. The Fitness and Pool area is quite okay. (Taxis from the Airport usually have a fixed / flat fee of 30€ indepented where you want to go in the city of Madrid)