The night trains are great. It's quite comfortable, you get there in the morning allowing for a full day (after dropping off your bags at the hotel) of work/tourism, and I especially hope Nightjet and other night train companies converts all of their trains to the modern mini cabins[0].
Comfortable and comfortable. It's certainly much better than spending a night on a seat. But most people won't sleep well. It's noisy and either too hot or too cold. The bed is hard, narrow and often too short for tall people.
I have spent many nights on trains in various countries, seats, floor and berth. I will prefer a couchette or sleeper if the price is somewhat reasonable. But I won't live in the expectation to get something comfortable. Just less uncomfortable.
Doesn't work for all of us. I can peacefully fall asleep from the noise of a CFM on an Airbus. On a train, rickety being chucked around all the time and always too hot, nope.
I can do 10h on a plane fine. 3h on a train does me in every time.
Unfortunately more expensive than a plane+hotel and has to be booked well in advance. It's worth the experience, at least for me, but it's not a real alternative.
When you said night train you can sleep on I assumed sleeper cars. But to be fair, I always looked at trains to/from Vienna, maybe that's the exception in prices.
Coach is a sleeper car, you just share the cabin with up to 5 people on bunk beds. Although on newer carriages (which I think is the one that goes to Paris) those are sleeping capsules where you have more privacy.
I took the trip to Vienna in one of the old bunk bed cars for 60€ and it was fine.
I liked the experience of chatting with the fellow passengers in the cabin that you usually don’t have on a normal train ride.
Sure it’s slower, but you’ll spend most of the time sleeping and it saves you one night at a hotel.
https://www.nightjet.com/de/reiseziele/frankreich