I've not been to Dublin or Zurich, so cannot comment on those (although I would love to visit Dublin sometime).
Of all the rest, Berlin would easily be my number one recommendation. It has the best proximity to Stockholm, and there is so much to do and see there. Obviously, there are a ton of museums, monuments and historical sites if you are interested in WWII and the Cold War. Going up the glass dome of the Reichstag is fun, for a view of both the Parliament and the city. If you just want to hang out in the sun with a beer, there are numerous cafes and beer gardens (or just grab some beer and snacks from the store and head to a park). There's tons of good food, of course. If it's your first time, I'd recommend
Prague would be my second choice -- it has a lot in common with Berlin in terms of great food, drink and night life, but it is also gorgeous and the architecture alone is worth a visit. Both Berlin and Prague are also comparatively inexpensive, which might be a good counterbalance to Stockholm.
I wasn't a huge fan of Munich, although it might be significantly more pleasant in the summer. It was cold and rainy when I was there, and I found it a bit boring. Ironically, it was also more expensive than Berlin.