transit choice montepulciano to venice when i already have a car rental - train or car?

Our philosophy is that if a train goes there, take it. It is much faster, safer, and more relaxing.

Let's look at the breakdown.

To take the train from Montepulciano-Venice is 5H33m

To drive is 3H58m, but you have tolls and fuel costs.

To drive to Florence, 1H30m drop the car 30m then train 2H05m...4H05m.

Only you can decide. It's all on the autostrada.

If you are not already visiting Florence, I would not choose that as the place to drop the car. Dropping it at a city that is on your destination list, such as Venice, means no detour. If you're not adding an extra day to the car rental to complete that drive to Venice, then the primary comparison is gas + tolls vs. train ticket prices.

I have done the drive and it is fine... not particularly beautiful, but since you already have the car you might as well calculate the cost factor and the fact that you can be on your own schedule, and maybe choose to stop someplace interesting for lunch on the way. You can then drop the car in Venice.
Often the weekly rate is far cheaper, so consider that into your figuring.

Dropping the car in Florence should not even be a consideration.

These are your only sensible options:

1. Drive all the way to Venezia and drop off the rental car at Venezia Piazzale Roma where all rental car companies are located.
   The drive is approximately 4 hours (nearly all freeway after an initial stretch from Montepulciano to the Valdichiana A1 entrance). The fuel cost about €45-50 euro (based on a car that gets about 13-15 km/liter) and the freeway tolls are €26.10 exactly. So the total cost is about €75.

2. Drive from Montepulciano to Chiusi in less than 1/2 hour (just over 20km) and return the car there. Avis, Europcar and Hertz have an office in Chiusi. The fuel cost is insignificant also because it's mostly downhill, let's say 2 euro. Then in Chiusi you catch a train to Venice. You will be required to change the train once. If you catch a Regional train from Chiusi, you would change to a Frecciargento in Florence. If you catch an InterCity from Chiusi, you change to a Frecciargento in Bologna. Either way the full train fare is about €57 per person. The travel time from Chiusi is about 4h30m, which added to the time it takes to drive to Chiusi from Montepulciano, makes it about 5+ hours.

The choice is yours my friend.

Roberto... any suggestions for them for a nice stop along the way for lunch?
Doesn't this route take you through Modena? I seem to remember stopping once and buying balsamic??

Folks - thank you for this excellent guidance. I appreciate the great detail. Still not certain which way we'll go, but doing drop off in Florence seems like an easy thing to avoid.

Thank you!