CX is a poor choice IMO because, apart from the extra stopover, you need to spend an extra ~6 hours in the air. In fact, NYC-HKG often overflies PEK.

In this case, if money is no object, then I'd advise the OP to go with AC (guaranteed flat seat) as long as the connections are nice. CO would be my second choice (good food and maybe a flat seat). I have a hard time recommending UA because: 1) ORD-PEK uses an old plane; and 2) BOS-SFO is 6 hours of unneeded discomfort.

That having been said, if money is a consideration, I would include double connection options, which are likely to be on better airlines and much cheaper.