During the pandemic (eg now per UA’s reduced service), their soft product is especially terrible. Meals are not something I partake in anymore in Polaris and the lounge is closed at SFO. Guessing LAX too if there is one. Hard product the newer US J seats are short and narrow. NH are too but their soft product is infinitely better. UA flights tend to be much more crowded right. Is due to more transit pax and military going into Japan as well as deadheading pilots. More pax means more Covid risk. NH flights are much lighter generally. I have flown every 6 weeks into Tokyo on UA and NH every month of Covid so I have a lot of datapoints. Feel free to PM with any questions.

BTW by far your best bet is to fly NH F on the 777 which they still run sometimes from LAX and SFO both to Narita (don’t think Haneda anymore just 787 which means no true F). NH F is orders of magnitude better than any UA product globally.