Kind of a poorly worded poll for two reasons. First, what do you mean by worst? Are you asking which is more evil or are you asking which works less effectively? If the latter, how do you define effective?
Second, the choices are categorized differently. It would have been better to ask, "Which is worst: Communists or Fascists?" or "Soviets or Nazis?". The reason being that Communism is a political ideology, whereas the Nazis were more of a political party who happened to be Fascist. Its kind of like asking, "Which is worst: Convertibles or Toyota Hybrids?" I said Nazis were worst only because they were a party that specifically carried out a policy of institutionalized violence under a coercive state - meaning they acted immorally. Conversely, the act of being a communist hurts no one. I think the Soviets were worst than the Nazis, and the Soviets may have been communists, but there is nothing inherently evil about communism. If a free people choose to erect and live under a system of communism, I wish them well. I wouldn't want to...though, it isn't like fascism (as we have in America) is much better.
I hope that was clear.