We've had a great time in Ana & Joao's apartment in Porto. Communication was very easy, and Joao was kind enough to wait for us late at night as our flight was delayed. He even prepared a little welcome snack for us which was lovely. The apartment has a great location, all sights are within walking distance, and it's just in front of a viewpoint/park where people get together to have some drinks and watch the sunset. It makes you feel like a local sitting there. The only downside of the apartment was the slanted walls, as a tall couple, we could not stand up in the bathroom/shower, and hit our heads in the kitchen a few times :D Normal-sized people would not have an issue though.
Thanks again Ana & Joao!