Of the 7 1/2 habits the one that I would consider the easiest is #7, teach or mentor others. If I have a general idea of how things work I enjoy sharing and showing others and I always learn more from my students discovery or my own discovery in ansewering question. Anytime you get prepared to teach you become more knowledgeable on the topic.
The hardest of the 7 1/2 habits the one that I would consider the hardest is #1, begin with the end in mind. Sometimes it is difficult for me to see the whole picture. I am a step by step person. Once I complete all of the steps then then I is see the WOW!