I highly recommend Raul's apartment. Located in a very central (yet safe) area, it is close to bars, restaurants, stores. Everything you need is within walking distance. The host is unbelievably helpful, and the apartment has everything you need for your (even longer) stay. There is an iron, hair dryer, drinks in the refrigerator, coffee, tea, and so on. The bed is very comfortable and the sunroom is a wonderful place to have your coffee and chill. If I ever come back to Porto, I will gladly choose Raul's apartment. I stayed there for almost two weeks and it made me feel at home :)