In Europe, I think of it like this:
Britain gave us the Bases, without their position bombing Germany would've been much harder. America gave us the supplies, without which many more would be dead from starvation, or being outright incapable of fighting back. The Soviet Union gave us the People to wash over the black mass that was the Third Reich.
You could do without one or the other. It would've been much harder, but it could be done. However, without all of the 'Big Three', the world as we know it would be a much darker place, a much sadder place. For all the atrocities committed by the Big Three(Dresden, the expulsions, the general 'Pillage and burn' mentality of the Soviet armies), we were saved an infinitely more horrible future. Only the most ignorant would say that Nazi occupation was better than Soviet installation of puppet governments.
Some of the acts committed by the Big Three were horrible, wretched, outright undeniably inhuman. However, it only goes to show how much worse the alternative was. I am a Prussian through and through, however I understand and accept that what happened was, at the time, seen as the only option. Irredentism of all breeds had to be utterly crushed, for we saw what happened when hate was allowed to fester in the hearts of a humiliated and bitter people who felt(rightly) they had been wronged by the 'Powers that be'.
All of you should be very well aware that I do not blame all of the German people for the atrocities of WW2. However, in order to secure Peace in Europe, or even, in the world, they all had to have been punished. Germany(And by extension, my beloved Prussia) was sacrificed at the altar in the name of Peace, a Peace which has been maintained since that day, for no war even remotely on the scale of the Second Great War has been seen since.
To sum it all up: Everyone played their part, everyone had a role. If you want to gauge it only in lives lost, the Soviets take first place. If you want to gauge it in strategic importance, Britain wins gold. If you want to gauge it in sheer scale of arms and supplies, America leads the way.