Train travel

Those cities are well-served by trains. What info do you seek?

Note also that bus transport is a growing approach. We have used Flixbus and found it pleasant. We did Frankfurt-Heidelburg-Frankfurt bus one way train the other. Also Vienna-Bratislava-Budapest may be done by some boats.

Here is the Hungarian rail company. You can use it as long as you are going to or coming from Hungary. I used to say buy from the country where the train originates and that may still be the best advice, but the last few times I have purchased tickets or checked for others the Hungarian site was cheaper than the Austrian site. Enough so that I would forget my advice. https://jegy.mav.hu/

To the best of my knowledge there are no longer any international transportation boats to Budapest and the boats that run up to the Danube Bend towns dont run after mid-September..

You are probably married to riding the rails but if part of the trip is Prague to Vienna to Budapest then it wouldnt hurt to look at a discount airline from Prague to Budapest then go north by train to Vienna and Bratislava. Saves a little travel time and can be pretty cheap if you pack light.

Not sure what info you want, but I am currently on a train from Bratislava heading to Prague and yesterday took the train from Vienna to Bratislava.

Can try to answer any questions based on my experience.

I can only speak for Frankfurt and Heidelberg of the places you've listed. As of today, the rail line between Frankfurt and Mannheim is undergoing major work. A number of the trains have been adjusted to busses, and every train I've been on in the last two months, to include trips to the Airport and Mainz, and south, has been late. The ICE between Frankfurt and Mainz was 25 minutes delayed, and that's unusual.

Plan on delays. Never plan to take the last train of the day. Look to see if you can connect through other cities if needed. Semper Gumby.