I agree that F class is quite nice on TG. But I guess your choice would depend on what's more important to you: Either TG's older seat, along with Excellent service, good food/beverage (including Dom Perignon, caviar, etc)--"The Flying Experience"......vs. NW's new seat, AVOD, yet only decent food and almost always forgettable, indifferent service.
Arrival and Departure times are almost identical; the F lounge in BKK is fabulous, and worth arriving early for, while the NW lounge at NRT is quite nice, a great respite from the crowds while in transit. Not sure about the TG lounge in KIX, or even if you need to de-plane in KIX in transit.
What you need to do is check to see which form of 747 NW is using when you plan to go. It switches a few times a year from 744 to 747-200. If it's the 744, it'll have the new, lie-flat seats with AVOD.
But if it's the 747-200, it's the older barcaloungers (just like TG's F seats, actually). In that case, it's an easy choice--TG. If it's the 744, then I would still go for TG, because it really does feel "First Class". But if you like your flat seat more than great service, go for NW. Have fun!