We had booked tickets on line for ICE21, running from Frankfurt Hauptbahnhof to Wiener Westbahnhof. This train left very early in the morning, but we chose it because we would not have to change trains at all. Getting to Vienna with all our luggage was much easier as a result of our getting up and going early.
The train was a Deutsche Bahn one, and the cars were very new. It was a great ride. It went as fast as 140 km/hr, so not as fast as the Spanish AVE or the French TGV.
If you book a ticket on line with DB, then you will have to show the conductor your printed ticket and the credit card that you used to buy it. This is different than the TGV from Paris-Est to Frankfurt Hauptbahnhof, where we had to present the printed tickets (purchased on line) and our passports.