I stood at this appartment for three months for work reasons. It was really nice, near the center of Porto, next to most of the most iconic places. The apparment was very comfortable and cozy, with everything needed for my stay. It had good internet conection (essential for my work), and had everything needed to prepare my own meals/breakfast. There are also some grocery shops nearby, making it easy to fill the fridge!
I would totally recomend both for short stays, and longer ones where you need to stay at the apparment for an extended period.