I'm wondering what the best way possible is to get from Vienna airport to Bratislava?
The easiest and simplest is by bus. Head to the exit of the vienna terminal and there should be waiting zones for buses. There's a couple of bus companies (blaguss, euro lines...) All go from the airport to the center. Should be every half hour between them... Wifi on board until you enter Slovakia.
There are two bus lines that run from VIE to Bratislava: Blagus and Slovak lines. I prefer Blagus because it has a stop at Novy Most (the historical center of Bratislava) rather than the Main Bus Station. Prices are about the same, less than 8 Euro. Both buses depart from the same bus stop outside the main VIE terminal (look for the exit by McDonald's). There is a posted schedule and generally one or the other bus will come every 30 minutes. It is about a 50 minute trip. Blagus is faster because it has fewer stops.
Here are the schedules of 2 companies that operate a regular bus connection between Vienna International Airport and Bratislava:
Blaguss (7,50 eur one way, the stop closest to city center is called "Bratislava, AS"): http://www.blaguss.sk/media/bratislava-vieden%20blaguss%2006.08.2012.pdf
Slovak Lines (7,70 eur one way, the stop closest to city center is called "Bratislava, Most SNP"): http://www.slovaklines.sk/fileadmin/user_upload/pdf/wien.pdf
Both leave from stops right in front of the arrivals terminal. Buy ticket from the driver, no need to buy in advance, they're never crowded.
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We just went to Bratislava from the Vienna airport in July and we found taking the bus to be pretty straightforward. You might select the bus line based on the location of your hotel/destination within Bratislava. However, please be advised that some of the the taxi drivers in Bratislava charge more than twice as much as the others. Our best result was to have the hotel (we stayed at Marrol's) set it up. Professional and reasonable every time.
bus from airport cheap and every 30 mins to center of bratislava
You can easily get a ticket at the automatic machines to Bratislava. Will cost no more than 20 euros.