Where is it best to have a Asian double eyelid surgery? China or the United States?

It is the surgeon's expertise and NOT the location that is more important. You should find the best possible plastic surgeon (see below link for helpful hints) nearest to you as medical tourism will not allow you follow up or treatment of problems.

I
recommend selecting a surgeon who is close to home. This will ensure that they can properly
evaluate you at each stage of your healing process. However, with that being said
your surgeon’s credentials do matter. You want a surgeon who is highly skilled
and who has experience with this type of surgery.

The best Asian eyelid surgery is with a board certified surgeon who has expertise in the procedure and can relate to your surgical goals. You can research surgeons and consult with different surgeons before deciding when and where to have surgery.