Realistically probably China as they are probably among the countries that depend the least on the US in terms of defense, banking, manufacturing, digital services, culture and the like.
If you want to live there is different question for a number of reasons, but I do think it is probably your best bet avoid the impact of a US collapse (which I think is very unlikely).
Regardless of what happens in the USA, a violent civil war in China is entirely possible within the next few decades. From a historical perspective those are by no means uncommon. The Communist Party has been able to suppress most internal dissent lately but when Chairman Xi leaves power anything could happen.
If you want to live there is different question for a number of reasons, but I do think it is probably your best bet avoid the impact of a US collapse (which I think is very unlikely).