The Google Play store is banned there, so there's no obvious "default" choice. Other than whatever your phone manufacturer preloads, which will probably be its own store, not necessarily a good store.

What are the alternative app stores available to Chinese iOS users?

It would be nice to have an App Store in China that didn't ban VPN apps.

There is wechat which is a 'superapp' that works almost like an OS with its own repository within the app.

To be clear, most of the alternative app stores here are so bad you’d never want them near your phone. They do things like slip spyware into apks and ask for broad permissions for extra stuff an App Store should never do, like “help you back up your text messages.” (This was in 2014 anyway, haven’t touched an android since)

Choice is good, but there’s something to be said for a locked-down ecosystem protecting consumers from bad actors. Not sure how to split the difference. I run linux on PC but have an iPhone because it needs to just work.