Paris to Rome - train or plane?

You don't say how long your trip is (how many days total), how many days do you have in Italy,
Are there certain things that you MUST do or see?
The train would be a lovely relaxing way to see the countries - but it will take a chunk of time
from your trip.
Sorry I can't answer your question - not knowing the big picture of your trip.
Hope others here can give you more info.
Happy Travels

plane.

1.5 hours

can be very cheap if you book well in advance

train trips over 5-6 hours get tiring. .. booking a private compartment expensive.. a shared bed cabin not fun.. and its not a restful sleep for most people.

Look at Vueling and Easyjet.. avoid Ryanair for this flight as they use an inconvenient airport for Paris.

Train! You will see the towns and countryside on the way and get the flavor of both countries.

Factor in travel time and costs to/from both airports, security lines, baggage fees, and then decide. I would not recommend overnight trains, but some people like them.

From Paris to Rome is almost 900 miles. By all means, take one of the budget European air carriers.

Travel by train sounds great, but not at those distances.

We went from Budapest to Vienna and later on to Prague this year by train. The trains were slow and uncomfortable (hot)--even in April.

It might depend on your travel style and how much time you have.

Is there a place on the way that you would like to see, or do you prefer to go direct?

I'm probably different to many, but next March my plan for a week in Rome is to take the train from London, and train back.

I thought about flying which would have been quite a lot less money and much faster, because I have a bit of time and there are a few things I would like to do on the way, with my stops in Paris and Venice, and probably Colmar or Affoltern am Albis.

Different people have different priorities.

Fly.
Cheaper, faster and more comfortable.
Trains are better for distances under 500/600 km, but Rome is too far from Paris.

I would suggest flying also with an asterisk.

On several trips (including one where I went from Rome to Paris) I did a long train ride relocation as it fell about 10 days into my trip and I wanted a day to recharge myself by just sitting and looking at the countryside. Depending on how long your trip is etc, I wouldn't exclude it automatically but it will chew up a whole day of your trip and most likely cost a good bit more than the quick and easy plane ride.

Fly! Don't waste time on a train. We are flying from Rome to Paris over the holidays, and our flight was only $90 on Vueling for a one-way ticket, and the flight is only 1-1.5 hours.

Thank you all for your replies! We have decided to fly so we can have more time in Rome. We only have 3 full days there. Thanks again!