With so many and such a variety of Great Wall locations, it can be difficult to decide where to go. While no one place is right for everyone, narrowing down some details will help a lot in deciding where you should go.
First, consider how much time you can devote. If you only have a day or two then travel to another city is not practical, so you will be visiting the Great Wall near your current location in China, whether or not that is Beijing.
If you have a longer time to devote, you have the option of traveling to your preferred Great Wall locations rather than being restricted to what's nearby. And if you're going for more than a day or two then you will be choosing whether to do a long walk or whether to do day hikes or short section hikes.
People often ask for recommendations for their first visit to the Great Wall. The best site to visit depends on your individual preferences. These recommendations assume that you are visiting from the Beijing area. If you are elsewhere in China (further east or west), there are many alternatives to these Beijing-area Great Wall locations.
If you're more interested in a full-scale tourist attraction than seeing the real Great Wall, Badaling is your best choice. It's crowded with tourists. It features a Great Wall that is rebuilt to better-than-new condition. And in addition to the Great Wall you can find all sorts of gimmicks from camel rides to toboggans.
If you want the shortest, easiest trip to the Great Wall, Juyongguan is your best bet. The driving time from Beijing is the least of any Great Wall location. And the Great Wall comes right down to the level of the parking lot, so you don't even need to ride a cable car or climb any long paths to reach the Wall.
If you have a little bit more time but still can't devote an entire day, visit Mutianyu. It's restored to an unnatural state like Badaling and Juyongguan, but it's more interesting and less crowded, and the scenery is better. And unlike Badaling and Juyongguan, if you walk to the end of the restored section, you can proceed to the unrestored areas, although this requires ignoring the signs warning you not to continue.
For those looking to see the authentic Ming Dynasty Great Wall, look elsewhere as follows.
The best place to visit if you aren't planning a lengthy hike is Jinshanling. It offers an excellent combination of interesting features, great scenery, and reasonably easy accessibility.
Another great place to visit is Wohushan. Wohushan differs from Jinshanling in being much less touristy and less developed. There are no facilities of any kind here. You can hike as far as you like (mostly uphill) and when you are ready, turn around and return (mostly downhill) to your starting point.
If you're interested in a one-day easy hike, you can hike either direction between Jinshanling and Simatai. Note: "easy" is relative. Hiking the Great Wall is not like a hike in the woods. See Hiking from Jinshanling to Simatai for details on this popular hike.
For a two-day moderate hike, consider hiking between Gubeikou and Simatai. In between, you can stay at one of the hotels at Jinshanling, or you can camp in a tower (or a tent) on the Great Wall. Be aware that hiking between Gubeikou and Jinshanling requires leaving and rejoining the Great Wall to bypass a military area, and you must prepare yourself in order to avoid getting lost. If you're pretty fast you can make this hike in one day. If you have extra time and energy, include the excellent Wohushan Great Wall in Gubeikou, and/or include the east ridge at Simatai.
A good location for a one-day advanced hike is Jiuyanlou to Jiankou pass. This is a strenuous and dangerous — and rewarding — hike. It will take you all day so start as early in the morning as possible. There are a couple of paths to Xizhazi from the Beijingjie and Yingfeidaoyang areas of the Jiankou Great Wall that would allow you to shorten this hike if you don't want to go all the way to Jiankou pass.
For a two-day advanced hike, hike from Jiuyanlou to Jiankou as above, spend the night at Xizhazi or camp on the Great Wall, and on the next day, hike from Zhengbeilou to Mutianyu. We recommend walking down the road at Jiankou and rejoining the Great Wall at Zhengbeilou. The Great Wall between Jiankou and Zhengbeilou is too dangerous to recommend to anyone but experienced rock climbers.
Anything longer than a two-day hike on the Great Wall is an advanced hike. There are really no easy long hikes on the Great Wall due to the terrain and the condition of the Great Wall. This is especially true if you want to hike on brick and stone walls since they are only to be found in the mountains. In the Beijing area, the only long and mostly continuous spans of the Great Wall are to be found in Huairou district between Longquanyu and Qinglongxia, and in Yanqing county between Bijiashan and Badaling. Any long hike on either of these spans is a great challenge in safety, stamina, and logistics.