The same poll has been useful for other certification exams, for me to get a better idea on which topics to focus when I write TechNotes and for others to get a better idea of which topics you may need to put some extra effort in. So whether you are currently preparing for this exam or already passed it, please let us know which topic you found to be the most hardest topic to study and of course feel free to motivate or elaborate on your answer.
For a more detailed overview of which topics the poll options refer to check the 70-620 exam objectives
here.