which is the hardest struggle of edmond dantes in the movie the count of monte cristo

The movie differs from the novel a little bit. It's been so long since I have seen it though. As this is primarily a literary site, I can comment on a theme which probably is reflected in the movie. I think his hardest struggle would be coming to terms with his own thirst for vengeance. Abbe Faria tells Edmund,

Here is your final lesson - do not commit the crime for which you now serve the sentence. God said, "Vengeance is mine."

The Count must contend with this all the way through the story.