How do you define evil and do you define it on different levels?

People say acts or people are evil, but they try to place certain acts or people as being more evil than another. For instance, is Hitler more evil than John Wayne Gacy, and he more evil than Timothy McVeigh, or McVeigh more evil than Luis Reynaldo (Tree Frog) Johnson, or he more evil then Martha Stewart, and her more evil then Bernie Madoff? What of those who worked the Soviet gulags torturing people daily in horrific ways or the nameless, faceless members of the Republican Guard that did the same, are they more or less evil in your eyes? What of the Coyotes who take the life savings of those trying to get into the nation but then leave them locked in a truck to die in the desert?