There are two main train companies which will get you to and from Vienna to Salzburg which is the route I took with OBB or the Austrian Federal Railway (the other is Westbahn for reference).
The journey took around 2 and a half hours and included the best train wifi I’ve ever experienced for free on board (yay!!).
Since I completely decided to go to Salzburg last minute and booked on the day it was a great deal more in price than if you purchase your ticket far in advance, which I would recommend doing to save money.
As I didn’t have a reserved seat I had to move around a few times when passengers got on but it wasn’t too big a deal.
The seats on the train are modern and clean, for such a short journey I was more than comfortable.
OBB has many regional services through out Austria with connections to other major European cities such as Prague or Bologna/Pisa.
All images: oebb.at
If you have a European rail pass then you can use it with their services too.
I was really happy with my journey with OBB and wouldn’t hesitate to use them again if I ever find myself back in Austria.