Having done both NW & KL routings to Europe, I'd say it's a toss up:
NW WBC via DTW:
- DTW is great/easy airport to connect
- nice WorldClubs in DTW
- A333's have power, good seats and I think improving service
KL WBC via AMS:
- 747 is cool, but seats are no where near new as NW's
- slightly better amenity kit
- slightly better wine
- you now have to go thru security again in AMS when connecting from Int'l (and the liquid Nazi's in AMS don't like the size of the zip bags LAX airports give out!)
- remember there is now an earlier LAX-AMS FL flight 3 days a week on a 777, new seats but WBC has a middle
LAX-CDG-FRA is not an option I've tried yet, but anxious to do. Just allow a DAY to transit at CDG as it's a freakin' zoo to connect.