My girlfriend and I stayed at Osvaldo & Susete's apartment for 4 days in January, right after NYE. The location is amazing, right off Rua das Flores. It's within easy walking distance of all the main points of interest in the city and has a ton of nice restaurants and shops close by. The apartment itself is very comfortable, tastefully decorated, I really can't recommend it enough: I would definitely stay here again if I come back to Porto.