But in terms of potential harm, unquestionably China, unless I'm actively breaking US law.
My hostilities with the United States government are an edge case, a risk to be managed. The government, for 9 in 10 people, is a good actor.
China is a foreign actor. Unlike the US government it has zero checks and balances which I control, and should it use this data to compromise our government or fool the people I live with I expect the consequences to be far more damaging.
They were caught not too long ago actually spreading environmental causes in Texas against rare earth mining. They were trying to leverage our political process to make us dependent on them. Tools like TikTok make them far more effective at these sorts of operations, and it would be incredibly foolish to trust them.