Of the places you have listed, I recently visited Prague - Cesky Krumlov - Bled, Slovenia - Split, Croatia - Dubrovnik, Croatia.
In Prague you can spend at least three days. There are many things to see like the castle and surrounding area. St. Charles bridge (though probably still under renovation), the jewish quarter, the old square and St. Wenzaslas Square. Food there is pretty good and cheap if you like beer and meat...lots of meat.
Cesky Krumlov is worth a night if you have room in your itinerary. There isn't a whole lot to do if you aren't going in the summer and can enjoy the lazy river - but it is very cute and relaxing.
Bled - this town was more resort-like then I was expecting. Very pretty, but we did take one day to drive the Julian Alps. Main roads will be closed in the winter. Lots of WW1 history in this area. Very good museum in a small town near the Alpine climb. Beware of car sickness...LOTS of winding roads. I mean LOTS! Hikes were beautiful.
Halfway between Bled and Split is the national park - Plitvice Park. Countless picture perfect waterfalls.
Split - ahhh, palm trees and sea views! The history of the Roman palace is just intriguing. The palace still exists, sort of...but inhabited by all the locals.
Dubrovnik - if you can make it, well worth it. Probably 3 hour drive from Split. The Serbian/Bosnian/Croatian war has a lot of history here. The evidence of damaged buildings is all around. If it is warm enough...dip in the Adriac Sea. Perfect ending to a trip. And there is a seafood restaurant in the old town highly recommended by RS. I can look up the name if you like...anyway - go! Get the fried calamari. Best I have ever had. The scampi was great too. We liked it so much we went back for lunch the next day. And a walk around the old town wall is a must for great views. That's my input. Good luck.
PS: in lieu of Budapest, I opted for Austria. Vienna and surrounding area is closer and it was great.
