I have been flying US<->PEK twice or more per year for the last 10+ years, however my experience is limited to Y so I'll post some tips should you choose to go that way.

If you choose to stick with flying economy I haven't found the experience to be substantially different between all the available options - in this case, I would fly whoever offers the best routing (assuming you have no status). Your one-stop options from FL will probably be limited to US and Chinese carriers: UA (via ORD, IAD, SFO), DL (via DTW, SEA), AA (via ORD), CA (via IAH, LAX, SFO, JFK), HU (via BOS, SEA).

UA and AA often fly older equipment to PEK that have limited entertainment options in the back (UA's 747s have wifi-based movie streaming but no power on most planes, 777s now have AVOD; AA's planes only have non-on demand entertainment). CA tends to fly newer or newly-refurbished aircraft to the US which have a decent economy product onboard.