Poland won 7 golds at four different Olympics and historically the best is Montreal 1976 when we had 26 medals - second most only to the Moscow boycott so that one doesn't really count.
For the post-communism era (also Soviet block collapse and all that) the best is Atlanta 1996 by far.
The worst? Outside of the two post-war OG when Poland was still in the gutter, the worst must be 2004 Athens. Only 10 medals in total, our worst total since Melbourne 1956. But in Beijing, London & Rio we only won 11 medals total so it's nothing to write home about.
Winter Games is much easier: best is 2014 Sochi, 4 golds & six total. Worst? Pick anything! Prior to Salt Lake City 2002 we've won medals at only three WOG - 1956, 1960 & 1972. The worst is probably Albertville 1992 - we had ONE top 10 finish all games - 8th in nordic combined