In a certain sense, Nazism was more evil, terrifying, and scarier than Communism. But this is because the Nazis, the way they did things, was on an emotional level extremely shocking and intimidating. But the Stalinists and Maoists were not better, just blander.
While in Nazi Germany you had fanatical SS officers doing things like personally executing or torturing people emphatically designated for destruction, when the horrors of Stalinism come up you simply have faceless bureaucrats taking random names from a list and purging the associated individuals. There were no exact "races" to persecute, just "class enemies" who could be anyone. In a perverted way, in the USSR and PRC everyone was given a "chance" to be the reddest of the red, while in Germany if you were a Jew, you were dead.
What looks scarier, Hitler yelling before a hysterical crowd while Panzer divisions roll east and west, or Stalin calmly sitting in a dull office checking off figures (people's names) from a list while smoking a pipe?
Now looking at the Holocaust and comparing it to the artificial famines, purges, and other atrocities of Communism, the Holocaust may look more brutal and purely evil, but perhaps it is because of this that it died out so easily. It was so repulsive on a gut "holy shit those guys will kill us!" level that everyone banded together to fight them and so after 12 years Nazism was done for. But what of the Communists? They did not actively invade other nations to export their purges, in fact, they killed millions in secret whilst resting much of their cause on the universal solidarity between all working men (which, ideally, was everyone). They did not preach the racial hatred that the Nazis did, but instead justified their killing as "being revolutionary". We all hear about stories from the Holocaust like Anne Frank's diary and the evils of Auschwitz, but who learns about the 40+ million victims of the Great Leap Forward? Even today many people believe the fiction that it was an accident. Who cares about the loyal Communists who were murdered by Stalin? Nobody does, and partly because many of those Stalin murdered were murderers themselves. Again, it does not conjure the same heart-wrenching mental image like what the Nazi Holocaust does.
In the end, my view is that the Communists are latent corrupters and killers of men, while the Nazis were the villains were worked with a high profile. Thus, it is Nazis who we think of as the universal evil and not the Communists even though the latter has created more deaths and arguably more suffering and civil deterioration around the world, over a greater time period.