What is the best time to visit China? Any suggestion on the places to go?

Well, China is nice for visiting all year round. Take Dec this month for example, it will be cold in Beijing, but warm enough in the seaside Sanya(https://www.travelchinaguide.com/cityguides/hainan/sanya/) in soutmost China and is the best time to participating in the Harbin Ice and Snow Festival(https://www.travelchinaguide.com/attraction/heilongjiang/harbin/ice_snow.htm). I think you'd better make the travel time firstly, or the selected China Tours(https://www.travelchinaguide.com/tour/default.htm) here will give you some good ideas.