I would highly recommend Rita and Helders apartment! It is located about five minutes from the Congress Center (perfect for those attending conferences). The apartment is on a very steep hill and is close to many wonderful cafes and restaurants. Belem is a ten minute bus to the west and downtown Lisbon is a ten minute bus ride to the east, and there is a bus stop right at the bottom of street.
The apartment was clean and bright. There is a washing machine that we used numerous times. Rita and Helder were exceptional hosts by answering many of my questions in the weeks leading up to our stay and giving us a ride to and from the airport. They provided us with recommendations on what to do and kept us updated for the week we stayed at their place. I will definitely be coming back if my travels ever bring me back to Lisbon!