Like Jorge I stayed at the hotel Gromada near the airport, as I was leaving next day for Riga. Very conveniently bus #175 stopped outside the hotel and took me directly to the Stare Miasto. So I was able to maximise my time visiting the WHS, first in the afternoon, then again early next morning.
I enjoyed seeing the imposing Royal Palace and the colourful baroque buildings surrounding the squares. But in addition there were the more sombre reminders of the Ghetto, the Nazi persecution and the Uprising.