USSR win about 90% of the war and ha 40 times more casulties than rest of the Allies. If there wasnt stuborness to resist in USSR, the darkness would still dominate Europe, and all of us would be living in nazzi countries. Stoping that makes them, but Ukrainians also, good guys in my book.
Would add Great Britain to the "stubborn" list too, and USSR human wave tactic is the #1 reason they had so many casualties. Still the fact that they answered the call and played their part to the biggest extent is indeed a good part of WW2 final result
I would temper this with the fact that, at the time, USSR was far-left and Germany was both far-right and expansionist, so its quite logical they locked their horns pretty hard.