Leon Trotsky without a doubt. Stalin was a paranoid, and incredibly idiotic leader. The only thing I can credit him for is defeating the Nazis.
Stalin was a paranoid blood thirsty mass murderer whose evil was only rivaled by Hitler. Trotsky, though his interpretation of socialism was too statist and authoritarian for my taste, would have been an infinitely better leader.
Trotsky is far better than Stalin could ever be, he would never have ordered the mass killings that Stalin did and would've kept the Soviet Union Communist instead of Totalitarian!
Trotsky was a key figure in the Bolshevik seizure of power in Russia, second only to Vladimir Lenin in the early stages of Soviet communist rule. But he lost out to Joseph Stalin in the power struggle that followed Lenin's death, and was assassinated while in exile.