Nuno and Telma's place is hands down amazing. It is modern, clean, and equipped with everything necessary for a great stay in Porto. Additionally, they take the time to walk you through everything you might want to see/do in Porto in great detail, and are also willing to provide help around the clock to ensure you have a great time while you are there.
The location is great because it is away from the major noise of the city, yet still close enough to easily walk or take public transportation to the hot spots. Can't recommend this place enough - don't miss it if it's available!