Been in Prague and Budapest, I live in Vienna for 1.5 years now.
Budapest I visited for the new year 02-03 and loved it. Hungarian people were friendly and helpfull when needed and not after your money all the time. In the city I noticed them to understand quite well english, but somehow more german. The Castle up the Pest side is amazing during sunset and the view to the city on the other side of the Danube is really nice. Compared to Prague/Vienna it's the cheapest.
Prague I visited in Easter 03 and it was also great. After Bratislava and Budpest I found it a bit expensive though. This also depends if you stay in the old city, where everything is more expensive. Get out of the re-builded old city and prices drop to 1/3. Beer&Food was just excellent. I also recommend to visit the Castle on the other side of the river. Again an excellent view of the old City.
Vienna... Well what can I say. I like it. There is definetely lot to see all these historical monuments etc. museums. Excellent food, culture lots of it. And also plenty of places to go out. The inner city is quite expensive, but there is as well lot of the the attractions. Fastest way to check most of the sights is to take tram 1 or 2 which are going around the city.
For the info of the cities I would recommend Lonely Planet (
http://www.lonelyplanet.com) I did my research through these. 2 weeks is enough to see most of all the cities, but as with the architechture they are quite similar one might get blinded at the end.
Feel free to ask more details.