There are hourly trains to Bratislava from Vienna that take 1hr 10mins and should cost around €15. I think return would just be double the single fare. But it's a regional train so no need to book a reservation just buy at the station on the day.

By bus, I've never done it but SlovakLines runs between the two cities in 1hr45. It looks like PostBus and Eurolines might also offer a faster service. Prices around €7-8.

If you fancy something different you can also go between the 2 cities via speedboat as they are both on the River Danube. The twin city liner takes about 1hr 15 and costs from about €19.

happy travelling!

Thanks loco2 for your imfo. Upon further reading, I found that there is a ticket call Euregio slovakia that cost 15euro return from vienna- brastiava and the ticket is also valid for public transportation in Brastilava. Do you know whether this ticket is still available? I found the imfo in OBB travel site.

Travelling via speedboat is definety out for me as i'm very prone to severe motion sickness.

Have taken both train and bus to Bratislava, personally found the bus more convenient.
In both cases you get off at the bus station or Railway station , both located outside of the center, we had to take a taxi to the center, as it was impossible to find information on how to take the local bus, and nobody spoke english.
Last bus to Vienna departs later than the last train, busses are leaving from Südbahnhof.

Hi
thanks clausar for your reply.