My .02....

It's a toss up. Being in NYC, the UA/US partnership would be useful, and I've read that both are pretty good about matching status. The biggest drawback to UA/US is the financial shape of both. Putting the two weaklings together won't make both stronger. AFIK, the employee groups on both sides are likely to start blaming the other for job losses after their bankruptcies. Codesharing doesn't create a lot of jobs, at least not in the short term.

But if you do any east coast flying at all, US would be better than NW. But as far as flying to the west coast, and Asia, they'll do ya just fine, and they appear to be much more sound financially. And besides, you can use your orphaned OP miles for Y seats on NW, and still get an Elite upgrades.

I tried AA this year as well, and while MRTC and a blocked seat makes a difference, the all RJ service to ORD sucks, and DFW connections make my trips to PDX and SEA longer than need be. Looks like it's NW for me next year...