I just flew the NRT to SIN flight yesterday on ANA in business. I am always pleased to choose ANA over United metal as the food and drink offers are superior (always opt for the Japanese selection and the French wines and champagne compared to United's mystery wine and sparkling wine). The ANA flight attendants are quite good.
I would splurge for the business class seat which is a fully flat seat. Where was only one person in the ANA first section, the seat is larger than the business class seat.
If transferring into NRT, I would opt for United Global First to gain access to the United GF lounge in NRT and likewise if transferring out of SIN, I would opt for Global First on United because you can gain access to the KrisFlyer First Lounge in SIN. I'm assuming the KrisFlyer business lounge is also good---just my preference.