I enjoyed staying at Carmo's place. It is not centrally located which is good so it's in a quite and safe neighbourhood. The metro station is only 10 minutes away and that can take you into town quickly.
The apartment is very charming and clean. The rooms have keys so you can feel secure and leave your things safely.
Carmo is a very sweet lady who provides so much tips and information about what to do and see in Porto. I would definitely recommend others to stay here