I *am* an AA Plat, and I agree with IP on this.

It can be summed up simply:

If you mainly fly domestic, NW is the way to go, over spending the money on AA upgrades to Domestic first (while you earn domestic upgrades on AA, if you mainly fly domestic, you won't earn them anywhere near as fast as you use them).

If you fly mainly international, AA is superior because you can use miles to upgrade from any fare (which, if your company is cheap, can be a good thing). NW upgrades internationally can't be done on the cheaper fares. And if you fly a lot of international, you'll be earning far more domestic upgrade "points" for your use.

Steve