We stayed at Sandra's place for 3 nights while in Lisbon. Her apartment is in an amazing location near Rossio Station and Praca de Rossio right in the middle of the city. It was extremely easy to walk around and see all of the major sights in Lisbon. Also if you're interested in doing a day trip to Sintra, you can catch the train from Rossio Station.
The apartment was spacious, bright, and clean. Sandra has stocked the apartment with all of the essentials. She has a hair dryer, iron, and many kitchen ingredients and tools (although I highly recommend taking advantage of the Lisbon restaurants!). The wifi was fast and the bluetooth speaker was a nice bonus. The only thing I would point out is that the stairs leading up to the apartment are a little narrow and steep so if you have big bags just be aware of this. There also isn't air conditioning, but the apartment is very airy and the temperature in Lisbon at night drops to a very comfortable level.
Overall if you are looking for an apartment where you can easily see all of the major sights Lisbon offers, you won't find one better than Sandra's.