funpig, i presume it might depend on which train. The only way to know with any certainity is to look at both sites.
EDIT: I got curious so I looked at one direct train in April. CD looks like more but includes a seat reservation. OBB with the seat reservation is the same cost more or less depending on how you do with the currency conversion. On the one train on the one day in April. RegioJet is cheaper than both of them.
For the one day that I checked RegioJet wanted 28.9 euro for 2nd class including the seat. But for 43.90 euro you can go Business class which is still cheaper than OBB 2nd class (depending on which train and the date) and with that you get:
The Business comfort class means premium service and maximum comfort.
Above-standard features with leather seats, entertainment portal,
Wi-Fi and priority service by our staff. Rajec water, Illy coffee,
juice or Bohemia Sekt Brut sparkling wine are provided free of charge,
as are newspapers and magazines. Our on-board menu with a variety of
snacks and beverages is available. The comfort of the Business class
is the best option for everyone who wants to work or relax during
their journey with above-standard service.
Refreshments, Air conditioning, Free water, Free hot drink, Power
outlet, Free juice, Steward, Wi-Fi, Priority service, Silent
compartment, Cancellation fees more than 15 minutes before departure:
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