Going by personal anecdote (well, by my grandmother who fled Silesia as a child): German refugees in late WW2 largely considered the Russians far more gruesome (violent, rape-y, etc, especially when drunk) than the British and Americans, although some considered their brutality justified by what they were hearing from how German soldiers (and the SS especially) had treated Eastern Europeans.
I'm guessing it's because Germans had racial propaganda dehumanizing Eastern Europeans (Slavs are "untermenschen") and the Russians retaliated once they were able to. They had seen far more gruesome behaviour by the Germans and had less inhibitions to treat them in kind. The Americans and British, OTOH, had merely been exposed to the far more "conventional" horrors of war (i.e. civilian casualties from war and occupation) until they found out about the camps.
As for the lack of atrocities committed by the West: don't for a second believe anything about the Pacific theatre of WW2 was lacking atrocities. Japan quite literally raped China, yes, but the US routinely firebombed Japan until they literally nuked city centres.
The fire bombing of Dresden (a German population centre) is considered a morally questionable decision these days. The routine fire bombing of Japanese cities is not even talked about. And whether you consider fire bombing civilians a war crime or not, the nuclear attacks on Hiroshima and Nagasaki most definitely were.
The thing to know about war crimes is that the legal framework for defining and punishing war crimes we have today (even if we make far less use of it than we should) didn't exist back then. There was no legal basis for the Nuremberg trials, legally speaking, other than victor's justice.
The reason no Allied (including Soviet) commanders or politicians were tried after WW2 wasn't that they didn't commit any atrocities, there were simply no international laws they could be charged for violating.
Note: I'm not arguing whether the way the US fought Japan worked or not, or whether the death count would have been higher or lower had they done it differently. I'm merely arguing that objectively speaking not only the "bad guys" have done horrible things to humans in modern wars. And I haven't even mentioned how the Vietnam war is perceived outside of the US.