If you are going to Madrid, have no doubts, stay at Nuria's apartment!
the place is amazing, extra new and rich furniture, fully equipped with everything you may need for a short vacation but also for a longer stay. Comfortable bed, bath room and kitchen, every detail has been taken in care here.
The location is definetely central, 5-min walk from Plaza del Sol, you have a lot of restaurants and bar all around.
Last but not least, Nuria is extremely kind, she made everything to help us not just for the check-in (directions, appointment, etc.) but also for the check-out (e.g she kept our luggages due to our late flight back).