I think it's safe to say utilizing mass murder to achieve any political goal, regardless of ideology, is reprehensible.
It's hard to say for certain. We have several examples of communist nations, including the USSR and PRC, which both committed massive crimes to achieve their desired political endgames. Those killed by communist regimes number close to 90 million.
The most prominent example of fascism we have is Nazi Germany, who certainly committed their fair share of atrocities in the name of their ideological system. Lord knows how many more would've fallen victim to the SS and the Gestapo had Nazi Germany actually won the Second World War.
I tend to find individual Communists less troubling than Fascists, simply because most Communists I've encountered are just naive and obsessed with "workers equality". Most Fascists I've encountered on the other hand seem to be more arduous in their nationalist and authoritarian beliefs.
If I had to pick, I'd say Fascism is worse, if just for no other reason than Communism, as a socio-economic theory, demands certain economic requirements that tend to lead to financial trouble and decline, in essence giving any communist regime a "shelf-life" before their centrally planned economy leads them down the path of ruin. Fascists on the other hand are more vague on economic matters and a bit more flexible/adaptable when it comes to such matters.
But that's just me.