I've always booked NWA fares thru nwa.com. You always have complete info readily available on the NW site when you do that. The only exception was the recent MR to Amsterdam when nwa.com (and Expedia) kept repricing my selections at $800+ instead of ~$240 as availability vanished. Travelocity.com was the only site I found that offered me a $240 Amsterdam ticket that I could actually purchase.

I book Delta thru Expedia (w/ my WP #) because the DL itinerary then shows up under my NWA reservations. However, when trips are booked this way my status never seems to up on my DL BP's.