I had a wonderful stay at Daniel's. His house is located in Bombarda, a very nice and lively area with plenty of art galleries. Not exactly in the city center, but quite close in a calm street with a few restaurant nearby (one is closing very late). It is 5 minutes away from the famous Torre dos clerigos, thus still close from all touristic spots!
The flat is vast, convenient and comfortable. There is all equipment needed and more! But, most of all, Daniel's hospitality makes everything easier. He spent some time to give local tips and advices, he is very resourceful!
It was my second stay in Porto and I definitively (and warmly) recommend his place!