Travel from Budapest to Prague

The terrain is flat and it goes along a river delta that's fine farmland. Looks somewhat like Arkansas.
Farms are beautiful to many people. I found the trip a little hot even in April, and the trains were rather slow.
It's up to you to decide which way to travel. You might want to check Czech Airline to see if the airfare is reasonably inexpensive.

David is probably describing some other trip. There is no ride around river delta. Which river? Farm fields are alternating with wooded hills and deep river valleys. Mostly fields and relatively flat between Prague and Pardubice, between Chocen and Brno wooded hills, deep river valleys, 11 tunnels between Ceska Trebova and Brno, few nice hills between Brno and Breclav then mostly flat but no river delta. Train is on so called corridor and speed while not as high as TGV or Thalys is certainly not rather slow. In average between 100 to 160 km/h. Scenery is nice but not spectacular and if pressed for time take an overnight train or fly.

I just found that I was describing direction Prague to Budapest, so just turn it around.

By the way why did you put your question under Switzerland?

I just drove the route in reverse a about a month ago - Prague to Budapest.
The drive should take about 3 1/2 hours but, because of heave truck traffic at the Hungarian border and a good deal of road construction where you have to cut your speed quite dramatically, it took a little more than 7 hours.
The route isn't particularly scenic. Lots of fields and forest with the occasional petrol station and rest stop.
I will say that the condition of the motorways in all three countries is very good, especially in the Czech Republic.
You'll need to buy a vignette for Hungary (unless you are renting a car there...it will come with the proper vignette), Slovakia (you'll pass through a small corner of this country on the way), and the Czech Republic. Some of the places to buy vignettes will sell them for just the countries on either side of the border they are located at, others will sell vignettes for multiple countries in the area.
If I had to do it again I would probably take a train or fly - a bit of an exhausting day but we were continuing on from Budapest and needed a car.

3 and half hours is absolutely unrealistic time. Not even professional car racer could do it. 7 hours sounds doable. Michelin says around 5 hours but that means without a stop and conditions must be ideal. In real world 6 to 7 hours. About the same as train but train is cheaper and usually without stress of driving in heavy traffic. If you are unlucky then driving could take much longer. For example once as I remember it took 5 hours from Brno to Prague. Colossal traffic jam around Prague.

Ilja, I was putting some post under Switzerland and forgot to change the country. Travel Forum virgin! lol