Himmler is both the most interesting and disgusting Nazi to me.
On one hand, he was the crazy guy with interests in history, paganism and kc tier theories. He financed "research" into the occult, let archeologists search for a lost Aryan civilisation, payrolled people like Julius Evola and wanted to create a completely new German culture. He invented traditions for his SS, made kc tier artifacts like the school rings, build or expanded castles... The craziest Nazi stuff you can think of short of Savitri Devi and Miguel Serrano - Himmler was your guy.
On the other hand, he represented what was the most evil and horrible about the Nazis. When thinking about war crimes and the holocaust, most people have this picture of the evil, sadistic Nazi in their mind who hates and enjoys bringing pain and death. This is how they understand the atrocities that happened. And such evil people existed and thrived during this time, of course. But they weren't nearly enough. Most people who contributed to the Nazi death machine were ordinary and decent people, who were misled into doing these horrible things. Himmler is exemplary for this and openly formulated his thinking about this in the (I think) Posen speech. When he oversaw mass killings, it made him physically ill. He didn't like it. He had to go to the doctor and took drugs or drunk to cope with it. But he felt it was important to do and found ways to make it more bearable, so he could keep doing it. And his SS men, too. This is the true horror of Nazi Germany, not just a few lunatics, but a whole nation led to doing horrible things against their natural instincts by a stupid ideology that wasn't even true.