Me and my boyfriend spent 5 nights in Diogo's apartment, the location was perfect, all the sightseeing are very close, 5 min. walk to Cais do Sodré (station to Belém, Cascais), the tram 28 stops in front of the house. The flat was clean, well equipped and because of the double windows, it wasn't noisy at all.
Diogo was very kind, he suggested us some incredible places (bars, restaurants, places worth to visit, not touristic places).
We definitely suggest Diogo's apartment, if you want to spent some perfect days in Lisbon.