Best day tour of Cinque Terre from Florence

I'm not sure a "tour" is necessary, as it's easy to do that trip on your own. It will be a long day though, so you might plan on leaving early and coming back in the evening.

Yes - easy to do on your own get there and back by train. Once you get to one of the five villages, you can get easily to the others by train or boat; there are frequent trains connecting the villages. Some hiking trails are still closed; if you want to hike, do some research ahead of time, closer to arrival (because trail status can change any day).

If you are looking for an organized tour I'm doing the Cinque Terre hike with walkabout florence in a few weeks. Can't say if it's any good yet but the reviews of this company seem to be great. We are doing a bunch of day trips on our own but want to do a few things with a group. This was one of 3 guided tours we are doing, along with Tuscany (same company) and Pompeii. Have fun on your trip!

It’s probably faster if you go on your own by train.
There are several trains that can take you from Florence to the Cinque Terre throughout the day.
At least one train change is required.
To see schedules go to the website below
www.trenitalia.com
Choose the English language option if you don’t speak Italian.
Enter Italian names of stations:
From: FIRENZE (Tutte le stazioni) which means Florence (all stations)
To: Vernazza (or any of the 5 Cinque Terre villages)
Date: choose any date in the next week if your travel date is beyond June 9 as Summer schedules aren’t loaded yet. The timetable doesn’t change much anyhow.
Hour: type a low number like 03 to see all departures starting early in the morning.
The main station in Florence is calle Firenze Santa Maria Novella, however I suggested to pur (tutte le stazioni), or all stations, because the fastest train to the Cinque Terre actually departs from the second main station, called FIRENZE CAMPO DI MARTE, at 7:38am. You will get off at the city of LA SPEZIA, and from there you can take any Regional train to any of the 5 Cinque Terre villages.

Florence to CT via train is an easy journey. However, keep in mind that train travel between towns can be a challenge. Expect large crowds and much jostling, especially if the trails are closed - which they frequently are. I would suggest travel to Monterosso al Mare first and backtrack from there. Or consider taking a boat from there and city-hop that way (much more pleasant) and end in Riomaggiore, boarding the train back to Florence from there.

Safe travels!