I think NWA.com does two things better than DL: recognize partner status and allow mileage upgrades online. The rest, I would tip almost everything in DL's favor.

As a DL elite, not being able to enter partner account numbers on delta.com doesn't have any impact on my life. Also, I don't use mileage upgrades currently and probably won't anytime soon. Thus, from my perspective delta.com is superior to nwa.com. I believe you will find many other DL elites have the same thoughts, but only because the website is so DL-centric.