A few more comments for consideration:

Star Alliance tends to offer far more flexibility in routing and rebooking options than Oneworld. Right now NH has two Chicago-Tokyo flights most days, UA has one, and JL has one. So as a NH or UA flyer you have three nonstops to choose from that will tie into your status and mileage earning, while as a JL flyer you are stuck with JL's single flight most days. The connection options also tend to be superior through Star Alliance. NH has daily overnight flights to Japan out of LAX and SFO, while JL has none and AA only offers overnight LAX-HND on certain days. Star Alliance also gives you the option to take SQ through LAX, or AC through Vancouver or Toronto, which can be useful for price or availability reasons.

United miles don't expire, whereas ANA miles have rolling expiration and need to be used within three years of earning. There are also high fuel surcharges on many award tickets booked through the ANA program.

ANA Star Gold status would give you United Club access when flying within the US.

United status would allow you to get complimentary upgrades on domestic flights (though the odds of actually getting these depend on status level, routes flown, alignment of celestial bodies, etc).