Eastern Poland wasn't founded on ethnic cleansing (or if it was, it didn't occur in the 20th century), so Eastern Poland.
What is now 'Eastern Poland' used to have the largest Jewish population on the planet. I gather that this is no longer the case. Of course it wasn't the Poles that did that, but then it mostly wasn't the Poles that removed (in an infinitely less evil way, of course) the Germans from Silesia and so on. Pretty much the entire of Central and Eastern Europe was 'founded' on 'ethnic cleansing.' Thank you, nationalism.
Killing half a million people is infinitely less evil than killing six million? That sounds more like a distinction of degree rather than a true moral difference.
Virtually all Jews who lived in "Eastern Poland" were murdered by the Germans. Special facilities were created to murder entire city populations of Jews. If individuals survived, it was because they escaped east in 1939, somehow eluded the Germans for five years living illegally (very few survived this way), or similarly were in the tiny minority who survived the camps.
The Germans who lived in now "Western Poland" were treated with extreme brutality and dispossessed, and large numbers were killed or died while fleeing west in winter. But the large majority escaped and started new lives in Germany as broke refugees.
The Germans who didn't flee in advance had some months to a year of Soviet invasion, immediate brutality, followed by dispossession and expulsion. The Jews had five to six years of German occupation, and nearly all were dead as a matter of policy within 3-4 years.
Both were "bad." But do you see the distinction?