We had a very pleasant stay in Mario's flat. It has a central location 2 min. walk from rua de santa catarina which is a big shoppingstreet, about 5 min. walk from the metro and right across the street u find a supermarked. The apartment was always clean and the cleaninglady so friendly. During our stay Mario recommended us a lot of things to do in Porto and was very helpful with everything we asked about. He even gave us his own, homemade map over the city.
The flat has everything you need! :-D