To go from Venice to Verona it is a good idea to take the train as it is the most practical and comfortable alternative (there is nothing to see on the way and Italian motorways are not exactly a marvel). It is not essential to book but it is advisable (see transport tab for more details). Take the train around 13.00 so that you have time for a last walk in Venice but also you can see something of Verona.
If there are more than three of you, it might work out cheaper to go by car, but it is still more practical by train. Should you want to go by car, hire it at Venice and leave it at Milan. It takes around 1h30min along the A4 motorway (around 7€ in tolls).
