It's hard to beat this location. Rafaela & Celio's place is only a 10 minute walk to Sao Bento (the main train station), and across the street from many bus lines. Their apartment is only around the corner from many bars and restaurants for the late-night crowd. Even if you just want to go to the Riberia, go port-tasting in Gaia, or see beautiful Portuguese tiles, you will be at MOST a 30 minute walk. We did not take the bus anywhere - we only walked every day.
The apartment itself was on a busy street, but the bedroom faces indoors, so it is nice and dark at night. The living room is tall and spacious, and there is plenty of room to relax.