If you want convenience then take UA which has a direct flight from ORD-HKG. However, if you are looking at mileage earning opportunties with AA, then I would recommend CX through LAX or YVR. They both have 747s operating to HKG and you can get an upper deck seat! I would avoid SFO and YYZ because CX operate A340s to HKG.

Or, you could book a round the world ticket which may be the same price or cheaper. You can fly ORD-LAX-HKG-LHR-ORD (plus additional stops in between) on AA/CX/BA. BA have the new business class sleeper seats on the HKG-LHR and LHR-ORD routes! Much nicer than any other business class that currently operate.