On long-haul transpacific C class, NH is definitely ahead of SQ. Service is more personalized and ANA catering benefits from F overflows so you may some entree (main course) selections identical to ANA F.

Unless SQ flies one of its new cabins flight, your ANA C seat will be about the same as SQ C. SQ has slightly better entertainment system with more selections but the NH's version is more than adequate.

SQ FAs speak better English however.

As for comparison against Northwest, there is no comparison. Northwest can't compete against top Asian carriers on quality.

Definitely go with NH C if you can.