A couple of points about buying a pass (kind of tangential to the OP's question, but hopefully useful):

1) The public water bus from the airport, the Alilaguna, is run by a private company. Its 24-hour pass (30 EUR) is good only on the Alilaguna lines, not on the normal city-run ACTV vaporetto lines within Venice. While the Alilaguna does have a few stops within Venice proper and to the lagoon islands such as Murano, it's much more limited and infrequent than the ACTV routes, so it's really useful only to and from the airport. It's actually cheaper to buy a round-trip Alilaguna ticket than to buy their 24-hour pass. If time is a prime consideration, note that the Alilaguna runs less frequently than the land buses (hourly versus half-hourly) and takes longer (about an hour versus about half an hour), but you can take it right to San Marco or the Rialto, for instance, without the need to change to a vaporetto at Piazzale Roma, as you would with the land buses. https://www.alilaguna.it/en/timetables

2) There are two brands of land bus from the airport to Piazzale Roma. The ATVO bus is non-stop and has a luggage hold, but is not included on ACTV passes. The ACTV bus has no luggage hold and makes local stops en route, but is usually only a few minutes longer and is included on the ACTV city+airport pass.