"Best" depends on what works for you.
Passes are usually not of much benefit in Italy- you have to do the math.
See what is covered and which venues you will definitely visit- add it up. Keep in mind that almost all venues now need prebooked timed entries.
For all venues- Use the official sites
Venice- a 24 hour vaporetto pass would be a money saver
I don't think any pass is going to be worth it for a 1 day visit.
You will need to book timed entries to St. Marlk's and Doges anyway. St. Mark's is just a few euros, not sure about Doges.
Florence
The Firenze Card can be a great savings IF your venue choices add up. You will still need to book timed entries for all the major venues- Uffizi, David, Duomo.
I don't think the Duomo couplex is included in Firenze Card
The transportation inclusion probably of no benefit- Florence is very compact- you wouldn't really need a bus anywhere
Rome
Roma Pass is the one most often mentioned- another that is probably not of much use. Vatican is not included., you stil need prebooked entries to Colosseum, Pantheon, Borghese, etc. The transportation component is probably not necessary for a short stay
Do some searches here on this forum
"Colosseum tickets"
"Uffizi tickets"
All of these things come up frequently and you will find posts with all the official links and info on how and when to book.
Be sure to filter your search by Type and Date
Here is a search for "Colosseum tickets" all threes from past 6 months
https://search.ricksteves.com/?button=&date_range=6m&filter=Travel+Forum&query=Colosseum+tickets&utf8=✓