the airplane you will be flying on will be Air China.
if you pay $265 or much more it will still be the same Air China 737. I think American may be partnered with Air China on domestic flights within that country.
another thing you may consider, I think strongly consider, fly a foreign flagged airline. Chances are the plane is newer, the routine maintenance is routinely done (easy to understand that ambiguity),
the service is much better.
to Beijing, I check Orbitz "3 days before/ 3 days after". My airline of preference is Air Korea (which is required to stop in Seoul) but the layover there is less than 3 hours. 2nd preference is Hainan Air. Korean flies Boeing 777s and Hainan Airbus A330s.
my wife is in Shenyang. That is where I go via Beijing.
on all international travel I fly foreign flagged airlines.
I fly out of Seattle. I am retired from Boeing.
I do hope that helps you in your quest for happiness.