Prague to Vienna .Bus or Train? Do you need tix ahead?

I always think trains are more comfortable. I don't mind a 60 minute bus ride, but more than that I will always take a train. As far as purchasing in advance, that is a personal decision. If you know your schedule, might as well buy it. There is a good chance it will be cheaper purchased in advanced.

Try looking at Regiojet.cz for the bus and price. They are a Czech company. They previously went under Student Agency. We used them from Bratislava to Budapest and the bus ride was lovely. They had TV with English movies, a bus attendant, and nice A/C. I believe the ride was about 3 hours and at the time - 2014 - it cost 9€ plus one extra for each piece of luggage they put in the hold.

All the info you need about the train option here: https://www.seat61.com/trains-and-routes/prague-to-vienna-by-train.htm

Train is faster and more comfortable. Going by bus you run a chance that you get stuck in traffic which happened once to me and we were three hours delayed on arrival to Prague.

I would recommend purchasing train tickets ahead of time and also getting a seat reservation. When we made the trip, the train got uncomfortably crowded. Next time, I would even consider first-class tickets for a little less chaos.

Agree with Ilja in that there are a lot of roadworks between Prague and Brno where you turn off for Vienna so more likely to have some delay. Also, in this case the train route is more scenic. If you go train and you want 1st class then that's best to reserve. If you're happy in the regular carriages then only reserve if you are taking one of the earlier trains that get into Vienna before 12pm because you'll have a lot of locals going down who work in Vienna during the week and come back on Friday (same with Student Agency).

I would also recommend the train and book in advance. We recently took the railjet train the opposite direction from Budapest to Vienna. We reserved our seats and we're glad we did. Our ride was under 3 hours. We booked 2nd class and were very comfortable. Keep your ticket handy when they do their checks. Passports were checked by Polizei before crossing the border.

I recommend taking a Czech Railways RailJet, rather than the yellow RegioJet train. The Czech Railways trains are newer and more comfortable, and the price is lower when booked in advance.