The convincing argument for Sergei Kirov
Well, to begin with, Sergei Kirov made a name for himself as a commander in Leon Trotsky's Red Army, leading the forces that defeated General Anton Denikin's Volunteer Army around Orel in 1919, and was a Stalin loyalist to begin with, and was recognized for it in the Mid-20's. it is hardly fair to say that he was a nobody, when he was brought in from Azerbaijan to run the Leningrad Central Soviet, a prestigious position at the time. Characters such as Lev Kamenev, Grigori Zinoviev and Abram Prigozhin were proto-Communist Party apparatchiks, martinets who were slavishly loyal to the Party and the Politburo. The were devoid of individual initiative, saving their talent for backstabbing for pure career advancement. They were dealt with accordingly.