burn and retreat method
Scorched Earth, deny anything useful to the enemy, including food, any form of shelter, etc.
I'll have to go with Stalin, Hitler killed 6 million Jews, but Stalin.... I think Stalin gets the title for Most Insecure, he killed so many even if they were just suspected of opposing him.. Osama, he lost his power in Al Qaeda a long time ago, while Stalin was in complete power and control until the day he died. Stalin gets the award for the worst.
Then again, I believe Mao Zedong was somewhere near 40-50 million, so he gets the Best Killstreak Award :P.