Hi Debbee,
The best weather is around April/May and September/October as the temperature should be quite pleasant. The winter can be very cold and the summer can be very hot, so its really down to personal preference.
The truth is that domestic tourism within China is growing all the time, so no time will be really quiet. However, our Holiday Creator plans the tour whilst dodging the Chinese National holidays, which are the main cause for major queues - so any of our dates should be relatively quiet.
I hope this helps.
Kindest regards,
Monty