Osvaldo & Susete have a great place! Super location right in the heart of everything in Porto. We walked everywhere and if you need it, the Metro is right around the corner.
Their manager, Mr Humberto, was waiting to greet us as we stepped out of the cab. He was so friendly and made sure we knew everything there was to know about the apartment.
The apartment is one floor up from a great walking street with lots of cafes, restaurants and shops (including the chocolate shop you can see from the apartment window!). Be aware though that you may hear other people enjoying the street late at night. The super window shutters definitely come in handy! :)