First and foremost, Porto is a great city and I'd recommend anyone to visit it.
Our trip was made even more pleasent by Liana and her nice appartment. She was very friendly and gave us some nice tips about travelling through Porto. Even though we arrived pretty late (12am), she waited for us with a nice bottle of Port wine. The appartment is clean and well equipped. It has two balconies, which we used intensively to chill in the evenings and grill on one afternoon. The area is quiet and in walking distance from the city centre (about 15-20 minutes). The tube station is just around the corner. Going through an old cemetery 500 meters away from the appartment, gets you on top of the hills facing the beautiful Douro valley. There's also a nice cafe / restaurant right across the street, which is open til late.