We really enjoyed our days at Barbara's place.
It's really well located, we arrived by metro and then we just walked around. In few minutes you can go down to the river or up to the hill, a perfect half way :)
The apartment has a big bedroom, a nice kitchen (with a good coffe machine!) and also a cosy living-room where you can have your breakfast, use your laptop or just chill.
In the neighborhood there are some good restaurants (vegetarian, Portuguese...) and coffees (where you can find delicious "pastel de nata").
Barbara is very nice, she gave us lot of informations, a mini guide with "10 great and cheap restaurants in Porto" and she greeted us with some good Porto! Thanks again, Barbara :)