A water taxi would be more spectacular but the train is cheaper and no problems at all.

Don't buy the train ticket by web! The train ticket from La Spezia to cinque terre should be few euro (abou 4 euro for a return ticket since it is about a 20-25 km ride) and buy it by the web will cost you more and more.

Moreover, it is not true you don't have to wait long time, there are local trains at least every hour and they haven't seat reservation service because are local trains.

Ciao, Marco in Milan - Italy