[ShopVac]

Obviously a car will not work in Venice. If taking there, they have drop offs in the town of Mestre - and easy ways to get from there to your destination in Venice. Venice does have an international airport that's not too bad (smaller size, less people). Note that in Zurich international, you can spend multiple hours in customs...similar in Amsterdam.

I've rented cars, flown, and done rail through out Europe. Rail system is pretty nice and convenient. Note that any rental you have, you will need to park...even hotels require some sort of payment for this in major cities. With the ease of Uber, I'd choose rail.

In any scenario chosen - try to pack as light as you can. Nothing more difficult that trying to cram large suitcases in the back of a tiny rental...or navigate with them on the trains.