What are you preferred carriers over the Pacific or Atlantic? Remember that you can earn NW miles on KLM but not on CO. On CO, you can earn CO miles on AF/VS code-share flights but not on NW?

If you fly first/business class (paid travel, not upgrade), I'd recommend CO the class of service bonus counts towards the elite-qualifying miles.

Welcome to NW/CO (and to the many problems you'll face in the future)