If you want to make the most of your stay in Porto, you should choose Bússola Oportuna Unipessoal's apartment.
It is extremely well located in the heart of the city, brand new, very clean and quiet.
Claudia and her husband are very accomodating and have a high sense of hospitality that you can see in their little attentions and care for the hosts and the apartment.
I definitely recommend!