Had the best stay at Manuel's appartment. He friendly welcomed us and gave us a lot of useful informations about the city and what to do.
The apartment is very well located near the praca dos poveiros where you'll find a lot of bars and the best sandwich restaurant in town: Casa Guedes, a supermarket and the famous shopping area of the city. It's also walkable distance from the bus and train station which will make your arrival/departure easier. It's also walkable distance from every major interest point of the city, in 4 days, we didn't take public transports once!
The apartment is really as seen on the pictures, small but very clean and well furnished, perfect for a short or a weekly stay for 2 people.
I would totally come back again and recommend staying there to any of my friends visiting Porto!