Both come at affordable rates considering the distance and both will leave you at major pick up/drop off points on the island city which means you will have to walk the narrow streets to your hotel or apartment if staying there.
An advantage of land transportation is you can exit the airport and board a bus more quickly, (especially in high season) than walking the 10 minutes to the water taxis and waiting in line for tickets and departure.
Land taxi’s to Venice from the airport can be found in abundance just outside the arrivals hall. The standard rate for a drive to Piazzale Rome or the Cruise Terminal is 50 Euros. The trip can take around 25 minutes.
The direct bus to Venice is 5-AeroBus, which takes about 25 minutes to reach one of the main Venice tourist terminals in Piazzale Roma. Your ticket where the ACTV boat lines travel to the centre of Venice.
The price for all the bus tickets to and from Marco Polo Airport is €8.00 one way, or €15.00 return, and €14.00 for the AeroBus plus boat ticket which will take you into the center of Venice, Tickets must be validated and are good for 90 minutes thereafter.