What was Polands greatest historical moment?
I'll go from left field and say the ratification of the Nihil Novi Statute (1505). The implications were earthshaking to the politico legal direction of Poland, and this Act was simply a revelation of the time when you think about it.
Fine battles aside, I think Poland's star shone brightest historically with its frighteningly moderns concepts of government. One could be tempted to say Poland paved the way for France, GB and USA hundreds of years later.