When a student asks "which subject is harder", are they actually asking "which subject is it easiest for me to pass with the least amount work".
Either way, it is impossible to answer. Your performance is dependent on so many things that only you know about
eg its "difficulty" depends on both your preparation and understanding of assumed knowledge
eg your ability to get marks might vary if you prefer exams or assignments
It is better to ask "which unit is more aligned to my interests and/or is going to prepare me better for next year at uni or my ultimate profession".
Students who are motivated and keen for a unit generally go better than those merely doing it because they have picked what is perceived to the "easiest" from a list of electives.