Travel from Ljubljana to vienna

Train

We took the train.
Slovenske železnice train to Klagenfurt Ostbahnhof in Österreich.
Then Österreichische Bundesbahnen to Wien.
The Slovenian train is open seating 2nd class.
The OBB train is reserved seating in 2nd class. We paid €80 on board to upgrade to 1st. Worth it.

Looks like you can take the train via Maribor/Graz or via Jesenice/Villach. There's only one direct train a day, via Maribor: EC 150.

I haven't taken the Flixbus to Vienna, but I have taken it from Ljubljana elsewhere. I usually prefer trains. My bus from Ljubljana (to Trieste) was late but was otherwise OK. It was only a 90 minute ride, though, vs a much longer trip to Vienna. I'd almost certainly take the train.

https://potniski.sz.si/en/vienna/

Hi. We did that today. Bought the ticket online last night from bahn.de. Train left Ljubljana at 8:15; easy change in Maribor about 10:00; arrived in Vienna at 2 pm. Comfortable and scenic. We brought our lunch and ate it at our seats, but there was also a dining car with table service and a menu of sandwiches, salads, snacks, wine and beer.

Bob, how tight was the connection in Maribor? It's listed as 14 minutes. Sometimes certain trains trains wait for connecting trains in case of a delay. Slovenia has had some rail issues recently and delays are common (were common before - both trains I've taken between Ljubljana and Zagreb were very late).

I once took the train from Salzburg to Maribor via Graz, so not quite the same route as Vienna but this was also a very pretty, scenic ride prior to Graz.

Hi Andrew. Yes, connection in Maribor was listed as 14 min. We were about 10 min late, but connection was very easy. Next train was already there across the same platform 10 feet away. A lot of people transferred so I'm sure it would have waited if needed.

Glad it worked out for you, Bob!