The Olimpia is a good choice for a larger hotel and there is also my favorite little place called the Ca Doge. Ca Doge is a very small inn-like hotel located right in the Piazale Roma (1 min walk from the bus). This little place has no elevators (not usual for small Venice hotels) and is very clean with a decent breakfast (included in rates). I assume you already know about the airport transfer options from the P. Roma. You can take the nice express airport bus (ATVO) or even grab a land taxi.