I spent a few days at María José's flat, which is nice and clean.
The flat is really easy to reach from the airport, and is at 20 minutes of the historic center by walk. And if you don't like to walk, there are several buses really close to the flat.
María José is really nice, she gave me some ideas of places I could see and where to eat.
However, there were no real curtains and the light of the street is really close... That is quite disturbing if you're used to sleep in complete darkness!