You can also pre-book terravision online - we did this, and it worked really well. In fact, even when I had completed the wrong dates, the company changed the tickets (after they should have been used).

Hmmm, not sure that the bus would actually beat the train if you didn't have to wait for the train.

Trouble is that the train from Pisa airport is a very short connection to Pisa Central (they'd be better off paving it over so you could walk to Pisa Central - it's only about a mile!) then you have to connect to a mainline train - so it's the wait that can cause the problem - one option would be to take a taxi to the Central Station and take the train from there. Overall - the locals think the train is faster. So you take your pick.