Ken
I don't know enough about Poland , but all 3 of the Baltic states have fascinating capital cities.
Latvia is the most"soviet" of the 3 republics, but ignoring the stalinist buildings there are some lovely Art Nouveau examples around the city centre and the embassies.
Estonia is perhaps the closest to the west , and the old town in Tallinn is certainly worth a visit, but beware of the British stag parties at weekends.
Lithuania is something of a mix between the two, but again the central area is full of really good old buildings which pre-date the Soviet era.
PS I have never been there in the Mog , only on business.