cruise

Huh? Could you please use a complete sentence to ask your question? And what do you mean by best? Fastest? Cheapest?

It's roughly fifty miles from the cruise port, Livorno, to Florence; less than half that to Pisa. Generally I prefer the train. Depending on where your ship docks, the train station can be walking distance - or not. It's probably best to grab a taxi to the train station after ascertaining how far it is from the ship. It's very hard to see Florence (Firenza) in a cruise day stop. Seeing two major sites is about all you can plan in a day (even with reservations). Train connections may reduce you down to a quick look around and one major site. You may want to rent a car to give yourself more time in Florence - which gives rise to concerns about parking and ZTL fines. If it were me, I'd plan for Pisa. Pisa can easily be seen during a cruise day stop from Livorno without rushing. Pisa's field of dreams can be done in two to three hours, leaving time for transportation, a meal and even a little shopping. One other choice, for the foolhardy like me, is driving to Volterra and San Gimignano for a short look around and lunch (probably not time for museums). They are in the fifty mile range from Livorno also. This requires a rental car and should not be attempted without a good GPS that you know how to operate.

I should add that I've never missed my ship - but I've been the last one to board before the doors close more than once.