Europe 2025

tmeyer0221,
Yes to Paris for at least 7 days! 2 days in Belgium (Ghent or Bruges). Or skip Belgium and add to Paris. I have only been to Prague, of your other choices, but I would pick Budapest, based on what I have read, for 6-7 days. Fly from Belgium to Budapest. Get open jaw tickets to Paris, from Budapest.
Have fun!

I would vote for 4 days in Paris (although you can spends weeks there) and 4 days in Belgium (2 in Bruges, 2 elsewhere). Of your eastern (really central) Europe options, I have been to all but Poland. With 8-10 days, you could see both Prague and Budapest but that is more city time and not much hiking (hikers, feel free to correct me if there are great nearby hikes to either city). If you want nature, I would pick one (maybe Budapest) for 3 days (highlights only) and leave the final 5-7 days for Slovenia (Julian Alps, Bohinj Park, Vintgar Gorge, Lake Bled, and tiny capital city Ljubljana). Use the forum search for more posts on any of these areas. Remember, you can always return and no matter what you choose, you are likely to LOVE it. Keep in mind that to maximize your daylight sightseeing, you might want to take night/sleeper trains. This would be fast-paced so if you want a slower pace (which most on the forum will advocate for), you will need to weed out someplace.

Brugges is great, but if you go to central Europe, you might skip it this time.

You need 5 days at least in Paris.

Prague is wonderful, also Krakow. Vienna and Budapest are great. You need at least three days in each city.

You have 11 days after Paris/Belgium. I would consider flying from Paris to Podgorica, Montenegro for the coast, the mountains, hiking, nature .... beautiful and inexpensive country. Then a flight to Budapest another inexpensive and beautiful location. Great mix of locations and activities.

Or less extreme might be fly to Budapest, get a short term apartment for the duration, and use it for day trips and 1 and 2 night trips. Lillafüred would be a good couple of nights for the nature and hiking. https://www.thecommonwanderer.com/blog/lillafured-guide.

And there are others.