The apartment at the Giardini Biennale is at the perfect location, if you want to see the Biennale exhibition. It doesn't get much closer than that.
The next vaporetto (boat ferry) stop is the Lido di Venezia, the beach island. So you have a short way to the beach as well. To the other side, you may walk into the city center and Piazza San Marco along the pier - with a beautiful view!
The area around the apartment seems to be mostly inhabited by locals and is very quiet at night. Easily the quietest room we had on our travel around the country. We had a nice stay at the apartment near the Biennale!