Done this several times on OZ and SQ; Above post is fully correct. You're best off going on SQ or OZ and credit it to CO (150% EQM). I've done several TPAC's on UA (ORD-NRT/HKG and SFO-HKG) and I can say UA's seat is cramped, catering lackluster, and service apathetic compared to OZ and SQ.

OZ runs QS seats on SFO-ICN which are quite comfortable, that combined with one of the best C soft products in the sky, I think would be the all around win.

SQ runs a 77W, which has nice seats, but they're a little limited in the functionality and reclining position, but excellent catering and service.

On this route I'd rank OZ>SQ>UA, primarily because I really like the OZ QS seats. OZ also only has 24 C seats on a 772 versus 42 on the SQ 77W, leading to much more individualized attention. IMHO, I think OZ flight attendants are less robotic as well.