score:2
Rossio / Chiado area are both very good options. And so is near Parque Eduardo VII though I have some comments here: If it's near the Rotund (MarquΓͺs), it's practicaly downtown, it's perfectly walkable. It's no longer than 10 min for Bairro Alto. You have the begining of Avenida da Liberdade right there and right after starts Rossio. You can find many (good) restaurants along the way. This is a very important and beautiful Avenue.
If it's in the upper part of PE VII, than you can add an extra 10 min to arrive to Bairro Alto or anywhere else downtown. It's, of course, walkable as well, but a bit more. It depends on your likes/dislikes.
Regarding subway: depending on where you stay near PEXVII you have several choices for the station: Marques, Parque or S. Sebastiao. Subway closes around 1AM.