Samantha's apartment worked out great for us. Three bedrooms were perfect for our family of 5, the apartment was clean, and the beds comfortable. That said, we didn't really spend that much time in the apartment -- we only stayed for two nights, and walked around Venice on one day we had in between, and for that the apartment is perfect.
It is literally 2 minutes from San Marco's (it would have to be on the square itself to be any closer) and about 10 minutes from both the Rialto and the Accademia bridge. This made it easy to explore the city in the morning, come back to the apartment for a few hours to recover a bit, and then walk around the city more in the afternoon/evening. I would definitely stay there again.