The Finns were incredible but nothing on earth compares with the Eastern Front and the inhumane barbarity that the average Soviet citizen endured from both the Axis and their own leaders. As a Brit im more than happy to concede 'badassery' to the Soviet Union. Imagine if the Soviet Union surrendered as easily as the rest of Europe? France(lol), Dunkirk? Singapore? the USSR wouldn't have stood for that.
And we in the west owe them enormously.
Without going too far into details and without discrediting the invaluable and heroic soviet war effort too much, let's not pretend that the soviets were innocent in this, they commited plenty of there fair share of heinous crimes on both German citizens, the people of Eastern Europe they were supposed to be 'liberating', and indeed their own citizens. Also you cant compare France to the USSR: if the USSR were the size of France, chances are they would have fallen even quicker.
Back on topic, personally I think the Poles are somewhat neglected of their badassery, putting up one of the fiercest resistance in Europe despite being one of the most oppressed, having entire cities razed by the Nazi's for example. Their exiled armed forces were the forth largest allied force in Europe (topped only by the majors) : they played a significant role in the Battle of Britain and pretty much all other commonwealth battles, and an often overlooked but very significant role on the eastern front too. At the end of the war, they'd lost roughly a staggering 25% of their population, more than any other nation in terms of percentage. Despite being a minor nation, they contributed a huge, almost disproportionate, amount to the war effort, with a spirit to just keep on fighting, even when everything was against them.
They're pretty damn badass if you ask me, if not the most badass.