Can anyone suggest the best way to travel from Pisa to Venice ?
Train, private driver, other ...

Best may depend upon how many people are making this trip together.

For me, I'd take the train. Chances are it would be one train from Pisa to Firenze SMN and switch there to a different train to Venezia SL.

Train. Unless cost is no object (private driver then).

trenitalia.com is the official train site for Italy. You will probably need to change trains in Florence. If your travel is not in the near future then the schedules on the site will not be active yet. Just enter your travel search for a matching day of the week next week to get a good idea of the schedule. If you are definite on travel date/time, you can get a discount for buying tickets in advance, but you may need to wait for the updated schedule.

Thank You for the advice. It is four adults traveling Sept 2014

The train timetables for your trip will become public in June of 2014. If you book ahead (for the stretch from Florence to Venice) you can score some cheap discounted tickets, so begin looking in June if you can lock yourselves into a given time on a given day. The stretch from Pisa to Florence is a cheap regional line and doesn't require or accept reservations.

Also realize that Venice has two stations, Venezia Mestre which is the industrial area up on the mainland, and the one you want, called Venezia Santa Lucia, right by the Grand Canal.

Pisa also has more than one station, you'll want Pisa Centrale, and in Florence you'll most likely make the switch at the Firenze S.M.N. (Santa Maria NOvella) station.