tidy

I am looking at traveling to China and adding on either Hong Kong, Tibet or both. I normally plan my own trips but am going with a friend and we will do an organized trip this time, I am NOT interested in planning one no matter how easy it is. We may travel with China Spree and would be gone any time between 2.5 weeks to 3 weeks.
When is a good time to travel..April, May, or September?
If you could only add one place would it be Tibet or Hong Kong?

Shanghainese

April and May are both good, October will be better than September.

You can't compare Tibet to HK, I'd definitely go to Tibet since you won't see anywhere like it not only in China but perhaps in the world.

thursdaysd

I would certainly rate Tibet as more interesting than HK, but which to visit depends on how long you have. You need time in Tibet to acclimatize to the altitude, and time to see more than Lhasa. You could easily spend all three weeks in China and only scratch the surface.

JPDeM

Weather will depend on where you visit but September will generally be better. Although May is good, you will most likely get a lot of rain in the south. Be aware of Chinese holidays around May 1st and the week of October 1st and avoid these dates.
Tibet and HK are totally different choices. It is up to you to decide which one is "best" for you. However HK is easier to visit. Tibet requires a special permit in addition to your visa and you need to join a tour (although it can be a private tour for 2). Tibet will be more expensive.

tidy

I think we will join a Chia Spree tour for 22 days that includes both Tibet and HK. If we love a particular area we can always come back. I think we will do September and avoid the first week in October.