Vienna - Bratislava - Budapest - Ljubljana

You'll need a highway vignette for Ljubljana [oops--meant for Slovenia], I'm nearly certain. You have to buy it (and I assume affix it to the windshield) before driving on Slovenian highways. I think Austrian has a vignette, too, but I imagine there will already be one on a car rented in Austria.

Do you really have enough time to take advantage of having a car by stopping off along the way? As Mister E has pointed out, the cost is going to be very, very high.

I didn't specify a time limit. :)

Thank you for the reply to the questions asked.

No, you didn't. But time available can make a big difference. Americans often don't understand what an impediment a car can be in Europe; parking can be very challenging as well as costly, and it's not necessarily available right near the sight you want to see. And American tourists, at least, are often dealing with severe time constraints that don't really provide sufficient time to see the major cities on their itineraries, much less smaller stops along the way.

I am going to assume you have already checked the one way drop off fee and found it acceptable. Clarify with the rental company that you are visiting all these countries.

English won’t be an issue.

I have only driven myself in Slovenia and Austria, and ridden in Hungary. I have no experience in Slovakia yet. Roads shouldn’t be an issue.

Be sure you have your vignette for Slovenia and Austria - and check on Hungary.

I have driven in Ljubljana and it’s not bad. Budapest is doable (I would definitely prefer not to) but parking will be an issue if your hotel doesn’t provide a spot. It will also be a bit expensive. If you are starting in Vienna, you shouldn’t have to worry about traffic and parking there. With a car, it may be difficult to stay city center so you will need to add transportation time to get to sights.

These are all EU/Schengen countries so hopefully someone can comment on border checks. I rarely drive from one country to another - but my actual experiences have only included EU to non-EU.

Budapest to Ljubljana is a longer day of driving. Perhaps you will have a night to stop in between?

Hopefully you have multi-city plane tickets. Although the drive Ljubljana to Vienna isn’t a horrible amount of time and would avoid the one-way drop off fee.

I would seriously assess what it is you want to see in between by car that makes driving a good option, since train service is mostly so easy in between. But if you have plenty of time, it’s doable - even if I wouldn’t want to (and I do drive a lot of places in Europe).

You can purchase the vignette for Slovenia on line. Check the other countries, you may be able to purchase those on line also.