Least worst ?
I have not flown any of those save A321 on Air China when UA cancelled my PVG-SFO flight and could only come up with this connecting to UA in KIX.
I asked nicely and they gave me an exit row (much to my surprise) on the relatively short hop, and that was fine.
My one word of advice is from my limited experience and from what's been posted, try to avoid PVG; PEK is better, not sure about the other cities where some airlines connect.