There are many differences between Hitler's fascism and Mussolini's fascism. The most significant difference is racial views. Hitler was a raging racist, who glorified the Aryan/Nordic race. Ironically, Hitler knew how little the Nordic people had achieved, and even chastised Himmler for digging up Nordic/Germanic ruins, stating that the Italians must be laughing at the Germans; for they were living in mud huts while the Italians were building an empire.
Mussolini's racial views were much less extreme and much more honest. Mussolini praised the Mediterranean race, which consisted of the Greeks, Italians and other related peoples. Unlike Hitler's Aryan race, the Mediterranean people had actually achieved something. Race was also much less important to Mussolini, who at one point had a Jewish girlfriend. It is unlikely that Mussolini would have committed any genocide if not for Hitler's encouragement. Mussolini was more than anything, a sad little man with an ego inversely proportionate to his size.
While Hitler was also a deeply troubled man with a big ego, he was much more dangerous. He hated the Jews because of his indoctrination into Germanism. He was most likely deranged and felt emasculated by the loss of his testicle during the First World War.
Another interesting aspect of fascism is corporatism. Mussolini's corporatism was much more radical and socialistic than Hitler's ironically named "National Socialism". Mussolini was a true corporatist, meaning he supported the merging of state and corporate power. Corporatism is in essence a throw-back to feudalism with some modern socialistic qualities thrown in. Hitler was a semi-corporatist who was somewhere in between corporatism and capitalism. Hitler, coming from a conservative background, was much less radical than Mussolini, who came from a socialist background.