Honestly, you might want to replace those totals into their time frames for a proper comparison.
Hitler (as Führer) : 1934 - 1945, or 11 years
Stalin : 1925 - 1953, or 28 years
Mao : 1949 - 1976, or 27 years
So Hitler reigned the least, and his "genocide impact" is reduced further when you consider that his Final Solution was not actually implemented before 1942. Beyond that, his Final Solution did not only concern Jews (something that way too many people do not know). You must therefor include up to 1.5 million Romani people, nearly 2 million Poles and up to 3 million assorted other victims (Soviet prisoners of war, intellectuals, homosexuals, Jehova's witnesses and other undesirables). Not counting the almost 20 million people who did indirectly because of his politics of deliberate starvation of "undesirable races".
So Hitler's direct "genocide total" is actually much closer to 12.5 than 6, and that in a time span of, at most, 4 years.
If Stalin had had that kind of behavior, he would have killed 116.6 million people instead of your quoted 62, and Mao would have killed 112.5.
Mao may appear to have done a bit less, but one must not forget that the population of China has always dwarfed the population of the Soviet block by a ration of around 10 to 1. In that light, Mao was positively benign.
In the end, let us not forget that all of these numbers represent the lives of millions upon millions of innocent people sacrificed on the alter of ignorance.