First off to note, I'm not trying to downplay the atrocities that happened under Communism, but I'm just curious about something. The majority of talking points pointing to the large deaths under Communistic regimes often look to The Soviet Union under Stalin, China under Mao, and Cambodia under Pol Pot. However these leaders were not the only Communist dictators that existed. Were killings in other Communist countries or other leaders as numerous or were these three a notable case?
Logically in terms of opportunity, Mao and Stalin had the 'advantage' of being in charge of countries with bigger populations than any other Communist regime. So it would be hard to 'compete' against them.
Pol Pot represents the other metric, and shows how murky the meaning of the numbers killed can get. Cambodia's deaths un Pol Pot weren't necessarily huge numerically, but as a percentage of the population his 'achievement' was still pretty atrocious.
Which brings the question of context. For example I suspect Romanians repressed by Ceaucesu didn't smile and say 'hey at least its not Stalin'. For them the devil they knew was more salient an example and personal.
Trying to figure out how many died during a period or as a result of a policy is valid and important. Start drawing comparisons and it can get weird.