Porto exceeded our wildest expectations and Marco's apartment was the best home base for our exploration. The apartment was in the heart of the city, but tucked down a quieter street. The residents there are friendly and you get a great feel for life there.
The apartment is terrific! Clean and accommodating. Everything was comfortable and we slept well (walking Porto's hills didn't hurt). The views coming and going from Marco's apartment were stunning, and it's in close proximity to tons of bars, restaurants and sites. We walked across the river to the port houses with ease, too. If you come in by train, it's super close to Sao Bento train station, too. Marco's place comes highly recommended.