My friend and I had a lovely time at Erasmo's apartment. It is small but comfortable and located in the centre, near every major attraction and transport links. It is on the fourth floor if this is something you need to consider.
Erasmo is a really nice chap, he was very easy to meet to collect the keys and he was always available. I wrote to him one morning after we got back from the festival at 4am and he replied straight away. Sorry mate, I didn't want to wake you up!
His English is not brilliant but good enough to get along. I would love to go back to his apartment any time. Lisbon is a great place.