train from Krakow

Yes but it was in 2009 I think. We took the sleeper train and had 2 two person cabins. The train pulled over in the middle of the night and the restroom was locked. It didn’t have air conditioning. The beds were okay. I didn’t sleep that well. The cabin was nice and the train fare was very reasonable. I might try a sleeper train in the future if I need to. We left at night and couldn’t see any thing until the next morning.

I wouldn't recommend the train as you have to go via Bratislava so it's not really the shortest route. The flixbus is about 3-4 hours faster from Krakow to Budapest.

But if you book in advance a flight will probably be quite cheap and a lot faster.

This connection is a good one both day and night since it is a direct shot, saving the transfer of trains when taking the day train.

The night train gets in at decent time. I would do either option day or night, roughly the same time duration either option. Both these cities are on summer trip, most likely I would do the night train option arriving in Budapest from Krakow.

There are direct InterCity trains (no 407 from Kraków Główny to Budapest-Nyugati, or you can choose other options with changes, e.g. in Katowice (for example BATORY/BATHORY train), Breclav, Vac or Vienna.