I can totally recomend Nuno and Telma's apartment.
These guys are the best hosts and made us feel very welcome and gave us great advice on what to see and where to eat etc.
The apartment is very cool with some clever design touches. As a location you can walk into the main tourist areas of Porto in about 20 minutes or grab the excellent metro which is just a couple of blocks from the apartment. It's nice to be a bit away from the hustle and bustle of the centre and chill out on the balcony..
Unforgettable weekend - thanks Nuno and Telma!