Hey there,
Congrats on your offers! WUSTL is generally considered the more prestigious school so if you also got more money there I would accept that offer! If you plan to stay in the US for at least a bit following graduation it won’t matter much that there are few Chinese students. You’ll want to gauge the strength of the alumni network at your target companies – that will matter more than whether or not there are many Chinese alumni. And a good job at a tech co in the US will position you well if you do ultimately plan to return to China once you get that US work experience under your belt.