I love the Great Wall very much. I have visited the Badaling Great Wall, the Mutianyu Great Wall, Jinshanling Great Wall and the Simatai Great Wall during the last three years when I worked in Beijing. I think the Badaling Great Wall is the most famous one and the nearest to the Beijing downtown. The Mutianyu is the less crowded section of the Great Wall.However, both the Jinshanling Great Wall and Simatai Great Wall are a little bit far away from Beijing city. Also, you have to do some hiking on these two sections,which might not be very easy to normal traveler. Choose the one that interested you most, you will never disappointed.