We are hiring a private driver for this stop, and I know it's quite trek to Florence (almost two hours). We've never been to either destination, and I'm wondering if we would be better off exploring Florence and saving Pisa for another trip, or will we enjoy both without feeling like we didn't see any of either? We are arranging tickets to see Michelangelo's David in advance.
Theresa, you don't say how long you have. I'd go for Florence and save Pisa. I loved walking around Pisa. If you have a lot of time in addition to the four hour round trip drive, you can swing through Pisa on your way back from Florence and have your driver drop you off so you can at least "see" the tower and basilica.
I agree with Sally. You really won't have time in the 8 or 10 hour layover to do both with any type of justice......
If you are stopping in Livorno as well, from La Spezia, just go and enjoy the Cinque Terre. If no Livorno stop, Pisa is fairly compacted for tourist sites, all in one main area. Florence could either take you a day or a week depending on your tastes. From La Spezia I would not try doing both Pisa and Florence, just concentrate on one. There is a lot more to Firenze than Michelangelo's David, the Uffizi, Pitti Palace, Santa Croce, Santa Maria Novella, Ponte Vecchio, San Lorenzo and the Medici chapels, Boboli Gardens...