To get from Vienna to Bratislava, I took the Blaguss bus. Here’s a link to the timetable from Vienna to Bratislava. The bus departs from Erdberg in Vienna, which is a stop on the U3 line, so it’s super easy to get to. You can buy a ticket online, on the bus, or at the bus station.
The bus station had large lockers for luggage storage, and there were pay bathrooms. There weren’t many visible food options around the station, so eat beforehand or bring food with you.
The bus itself was large and comfortable. The bus had free wifi, and it departed on time.
From Erdberg station in Vienna, the bus stops at the Vienna airport, the train station in Bratislava, Novy Most (near the UFO bridge in Bratislava), and finally the Bratislava airport. The bus we took adhered very closely to the timetable.
A one-way ticket was only 7,50 euro, and it’s perhaps much more convenient than the train depending on where you want to go. For example, our hotel in Bratislava was just steps from Novy Most, which meant that the bus saved us a transfer at the Bratislava train station, in addition to being cheaper. Definitely an option to keep in mind if you need to get between Bratislava and Vienna!