Germany, the Czech republic, Slovakia, Ukraine, Belorus, Lithuania and Russian Federation.
Well I live in Canada and havent been to Poland in over 15 years but here are my opinions.
Germany: I think Polands relationship with Germany is on fairly good terms
Czech and Slovakia: Czechs and Slovaks I cant really say. They are very similar to us in some matters.
Ukraine: I dont have anything bad to say about Ukraine really. East Ukraine is mostly Russian speaking and some of them wouldnt mind rejoining Russia. West Ukraine is mostly Ukraine speaking. They are quite nationalistic.
Belarus: I am not sure.
Lithuania: I personally have no problems with them.
Russia: is a VERY complex situation. Either Poland has to have aid from the west or from Russians or mix it somehow -_-
(If I have any misinformation please correct).