Famous professor at relatively unknown university for post-doc
Just opinion, of course, but I would suggest that a great professor at a small school, no matter its reputation, would be a huge asset. You will have a chance to work closely with a mentor that you wouldn't get to do as well at a larger place. I realize of course that size and reputation aren't necessarily the same. 

But it is the letters you get from the professor if they are well known that can set you off on your career and, if you do get the chance to work closely, that association can pay dividends for a long time. 

While a degree from a prestigious place has value, I think a postdoc with a leader of the field is a great asset. 

And, of course, "relatively unknown in central Europe" is itself relative. Lots of people don't know about, for example Charles, and such, depending on where they are from.