Palestine, though I think the idea of which side is more sympathetic is unduly binary.
After World War II, there was a clear moral and practical impetus to create a Jewish state or homeland. While that form should never have been an ethno-state as it became, there still was a need to grant something like an Israel.
But there was no reason why the crimes of Germans (and other Europeans) should have been paid for by Palestinians.
Palestinians found themselves pushed off of their land to service people they had not met who they had not injured in any way. That is a colossal injustice.
I tend to find myself identifying with the underdog, but in the story of Israel-Palestine, the issue is that there's a way of viewing both as an underdog. Israel is a majority-Jewish country, a people who have endured a tremendous amount historically across the continents, in a region of Arabs, Berbers, Persians, Sudanese and many others, most of whom are Muslim. Palestinians, meanwhile, were under the heel of British colonialism before they found themselves being smashed by nationalists of a new ilk.
It may be this fact, that both sides are sympathetic for markedly different reasons, that makes it such an ugly and divisive conflict internationally. We're story-telling creatures, and while it's not true that all of us identify with the underdog (there is a large trend in our behavior to identify with the victor not the vanquished), in the case of Israel and Palestine one sees two peoples trying to survive in a small strip of land with limited water. Both sides have had ugly nationalism informing their politics.
Still, at the end of the day Palestinians did not start the conflict and did not move into the lands held by Jews. Like many refugees to what is now the United States before them, Israelis moved from being victims of repression to themselves being violently repressive and brutal (even as the repressive and brutal states around them seemed to target them, an additional rub). At that point, when many of these individuals moved from victims to conquerors, my sympathies left them.