China is a country with so long history that you cannot see all its magnificent sights and wonders for one time. So the perfect itinerary should depend on your interests and the time you stay in China.
If this is your first time to come to China, Beijing, Xian and Shanghai would be the best cities to visit. You can experience the ancient China in Xian, the present China in Beijing, and the future China in Shanghai. You can go to the famous Mt. Huangshan, Lijiang and Guilin if you want to view the beautiful natural landscape. Mystical Tibet will show you not only the natural spectacles, but also the vicissitude of Tibetan Buddhism.
If you mean to understand the ancient culture and history of China, the Silk Road Adventure will not make you disappointed, the fascinating overland route once used for transporting silk etc to Europe including little-traveled parts of central China and pass through archaeological treasure houses of Xian and Dunhuang, heading into Xinjiang.