We are trying to plan a trip to Vienna, Prague, Budapest, Warsaw?

When it comes to quality of food, Czech tends to better than German or Austrian. Hungarian food is better than Czech or Austrian. People who whine the most on Czech or Central European food are individuals who tends to like too much green vegetables as these cuisines put emphasis on sauces, steaks, meat, pork, sausages, cheese, dairy, and sauerkraut washed down by wine or beer. However, there are McDonald everywhere so, you can stick to common junk food you find in USA. This what Americans usually do, go to McDonald, KFC, Subway, and Starbucks; and many never will try local food even if served on silver plate for European nobility.

I would skip Warsaw, and would choose Krakow. Warsaw is too far from Prague, Vienna, or Budapest and not easily accessible by train as is Krakow. There is good connection between Vienna and Prague and Vienna and Budapest. Budapest has many world class restaurants and food is more spicy. Pricey restaurants offer the best experiences there as do in Prague. Vienna is unique. It has some super expensive places, but the city is literally deserted on Sunday and you may have hard time to find anything open except Fridays and other chain stores. This is difference from Prague and Budapest that have night life and where you can walk to any high end restaurant in 10pm without problems. Krakow is smallest from all the cities, but there are some good places to eat in the old town. Pastries, cakes, desserts are feast. The best choice is in Vienna, followed by Prague. Quality of services differ, but Austria has generally the most efficient staff, followed by Prague, Poland, and on the end is Hungary where service can be rather slow. As anywhere in Central Europe servers are not overly friendly, but they do not bother you every minute like in USA during dinner if you need anything.

Eastern European food has certainly improved since the Soviet Union days. There's a variety of restaurants in all those cities.

It gets very tricky, though, if you try to drive through all those countries. Check with the rental agency first and make sure it's allowed. It's easier to get around on the trains.