We've spent 4 nights at Sergio's place.
The appartment is really nice. Its location is perfect - almost all sightseeing places are in a walking distance.
Sergio is a great host. He picked us up at the airport and gave a lift to the appartment - we had a possibility to talk about the city and life :). He cared about us, offered to go out for a dinner together and gave many useful instructions and advices.
I can highly recommend you staying at Sergio's place.