Everything about this location is superb. It's centrally located, with some great breakfast and dinner spots within a stones throw. We walked everywhere from the apartment, which is exactly what we were aiming to be able to do. Joana's mother was also a very pleasant host, greeting us upon arrival and taking great care to show us all the recommended sites and places to eat on a map in the apartment.
The only downside we experienced was the random shouting and chanting that took place almost every night and into the early morning. The apartment is right across from the university, so we're not sure if this is a normal occurrence or if there was an event going on that had everyone all jazzed up, but it did require snug earplugs.
The noise aside, if you're looking for a centrally located apartment in Porto you can't really go wrong with Joana's place.