We will be traveling from Nice to Paris in early September. We only have two short nights in Paris, so I am wondering if it will be the best use of our time to fly or take the train?
I would fly.
Do the math for both fares and time.
Fly: 2 hour check-in + flying time + potential flight delay + transportation to your hotel
Train: 20-30 minute arrival before departure + train time + transportation to your hotel
I agree with JeanM's formula for deciding. I'd also consider:
1. What will your vacation have been like to that date. If hectic, you might prefer the train to relax. If not, plane or train?
2. Environmental factors: train is much friendlier to the environment. How does that fit in this particular instance for you.
3. Do you want to see the scenery between Nice and Paris? Then train.
4. Would you like to relax and enjoy the trip or just get there? Train vs plane. (OK, this might be too close to 1.)
You're not saving much time by flying so I'd suggest the train. In addition it will give you some great views between Nice and Marseille.
sitting on the right hand side upstairs gets views towards the end that are fabulous - no flight can compare.
After the train reaches the coast it is on normal tracks so slows down, more time for the views.
The early train from Gare de Lyon (around 7:30 if I remember correctly) is one I have done several times. Never fails to be pleasant. And gets you to Nice Ville at a good time of day.
Will you be staying in Nice itself or nearby?
I took the train and agree with the other comments about the train. I did purchase a business class since I was traveling solo, so I could have the one seat vs. two seats in a row across the aisle.
Environmental considerations aside, I would fly to Paris Orly airport. The airport in Nice is max 30 min from downtown, and you need to get there ~90-105 minutes before your flight. Then it's a 90 minute flight to Orly, max 30 minutes to deplane and reach the metro station, and a 30-45 minute ride to central Paris.
Total time max 4 hours, vs. 6.5 by train including some buffer at the train station.
In other words: a morning flight gets you to Paris for lunch. That's impossible by train.
If you're a transportation history/fan, look up the story of the train route from Paris down to Mars. et Nice, and that might also be something you want to join. OTOH, you can never have too much time in Paris.