Nice place in the region called "Estrela". From there you can walk almost anywhere, because Lisbon is not a big city at all. The flat is located in a very safe road, between the British Embassy and an official government residence, although Lisbon is generally safe anyway (we walked a lot and never felt unsafe).
The flat had a washing machine, which is useful if you like to travel light. The kitchen had oven, hob, kettle, fridge and microwave, allowing us to cook for the kids when they got tired of restaurant food. The flat is located on the 3rd floor, and there is no elevator, but that didn't bother us.
For those travelling with children, there is a nice garden with playground just around the corner: "Jardim da Estrela". You will also find close by a supermarket ("Continente"), a bakery ("A Padaria Portuguesa") and many ice cream shops.
I'd stay in Maria Rita's flat again.