Well, since you're travelling with a child (you didn't mention his/her age) then the direct PR flight might be more convenient. Their flights are also at night, so hopefully the young one will just fall asleep. With the other 2 carriers if there is a flight irregularity you risk misconnecting or being delayed at the transit point. I once had an extended delay at NRT due to a snow storm a few winters ago, had to spend the night in a hotel at NRT, but but never left my room since I had no winter clothes (I was returning from Malaysia). I'm also not too keen on PR not being partnered with a U.S. carrier.

The thing I dislike about NW is that their SE Asia departures are at a very early hour and their arrivals there are at a very late hour. I don't know how this might affect your travel routine with a kid in tow. Personally, I'm not too fond of NW's transpacific in-flight service, some of their senior F/As are down right scary! Maybe they'll be on vacation during the holidays and you'll luck out with a more junior crew. However, if I desperately needed the miles at the end of the year to maintain status (OnePass Platinum) I wouldn't hesitate in flying them.

In any case, I hope you enjoy your holidays in the Philippines. The father of a friend of mine was assigned to the U.S. consulate in HKG about 20 years ago and would always take the family to MNL in December for the Christmas holidays.