Similar to servers for Mainland China, this article assumes that you won’t be able to get an ICP license. If you can, then please get in touch with developers who can help you in Mainland China directly.
Savest solution
The savest and in most cases best solution is to not have a CDN. This goes contrary to what most developers will tell you, but for Mainland China, it is the easiest way to make everything work.
The main reason is, that your server has 1 IP address, if that one works in Mainland China, everything will load.
CDNs have varying IP addresses and load from different locations and servers, which introduces a lot of variables and uncertainty.
So if you want to play it safe, go with no CDN.
What about Cloudflare?
If you have to pick a CDN, Cloudflare or Alibaba Cloud might be the best ways to go. Both have extensive connections to Mainland China and it’s therefore least likely you’ll get into trouble (though not completely impossible).
When you do your research around China and hosting, you’ll most likely come across Cloudflare Enterprise with their China CDN. This is a great solution if you are a multi-national company with a location in Mainland China (and a ICP license). For SMEs, this is probably not the way to go.
Alibaba is a nice way to go if you target mainly Southeast Asia. You could host your website in Hong Kong and use their CDN. You won’t be able to use the Mainland China nodes of the CDN, but the ones in Hong Kong, Taiwan, Japan, etc. should all work well.
Worst CDNs for Mainland China
The by far worst CDN is the one provided by WordPress.com and the Jetpack – if you use that, you can be sure the website won’t work in Mainland China.
From experience, AWS works sometimes, sometimes not. Google Cloud in general works surpisingly well, even though it’s from Google.
However, as mentioned in the beginning, if you can, avoid CDNs altogether.