We stayed for four nights at Luigia's lovely apartment which is just a short walk from St Mark's Square and the San Zaccaria vaporetto stop. Luigia's map was invaluable for finding the apartment, even though we still got a little bit lost which is normal in Venice. The best boat line from Piazzale Roma to the San Zaccaria stop is either the 4.1 or 5.1 (and the 4.2 or 5.2 on the way back) as the others take much longer.