I would be very happy to recommend Anasus' place.
The location is perfect: you step out of the door and in a couple of minutes you are in the heart of the Bairro Alto, with all the most vibrant nightlife; but once you've had enough fun you can sleep well as the building the apartment is in and just around is all residential, so it's much more peaceful. From Bairro Alto you can walk easily to Chiado, Cais do Sodre, Principe Real, Baixa etc, and are near the tram and metro.
The apartment itself is pretty and comfortable, spotless, and with everything you need for a city base and the building itself is well kept.
Anasus is a lovely person, very friendly and seems to really care that everything goes well.
We had a great time and miss Lisbon already - thank you!