Both governments claim that they are incarcerating criminals.
Both governments claim that the incarceration is for reeducation, but we know that the US makes zero attempts to reeducate anyone in prison, given the extremely high recidivism rate (70 to 80% depending on where you look) and how the US government(s) put roadblocks against ex-con to keep them from getting jobs, housing, etc. which means they have little choice but to turn back to crime.
I don’t personally know what attempts China makes to reeducate those who ends up in prison. Some in depth research is needed and even if I do find their statistic on recidivism or lack of it, many will say official stats from China is fake.
What I DO know is that China makes no claim that it is a free country, or what rights you have. So you go into China knowing that there are rules, and nothing is off the table when it comes to rules. The state can prohibit you from association, from joining certain religions, from saying certain things (that are not fighting words or any unprotected speech). The state can also monitor any and all communications as well as prohibit you from watching certain contents, websites, and have systems in place to enforce that.
We also know that the US does all of these, yet the US claims that all people have certain rights, outlined in their constitution, yet in practice they are routinely ignored by Congress or the government in general when it suits them. We also know the US has questionable election system or laws that favors incumbents, as well as a two party system that are not really opposed to each other.
This means a layperson (as in someone who isn’t a lawyer or studies US government) goes into the US believing that they have all these rights, when in fact the government either currently allows certain rights, or that the person is simply not on their radar. However once you are on their radar, and if the wrong person were annoyed (not pissed, just annoyed), there are enough laws in the books that the person can be summarily arrested and/or deported after serving a sentence.
That same person will go into China knowing that there are no real rights except for what the government currently allows, and will act carefully in order to avoid triggering the wrong person and saying the wrong thing. He might actually have better success in avoiding the government’s radar.
So you decide which is worse…