Soprano's Loft is the perfect place. They are the perfect hosts, who solved the problems that came up as quick as it was possible. The apartment is very well located. It is on a popular nightlife area, but on a quiet street that keeps you away from the noice. There's a supermarket near by, and a lot of restaurants to have typical portuguese food.
The place is perfect for two. It has a very comfortable bed, and has everything you'll need to have dinner at home some day. For instance, it was very very clean. Having the shower separated from the bathroom wasn't so convincing at first sight, but it's so practical because everybody will keep their intimacy if the both of you want to use the bathroom.
We will repeat if we'll come back to Porto, for sure