CO OP counts segments towards status, NW WP doesn't. So if you do alot of shorthauls, CO is the way to do it.

I do mostly domestic, mostly shorthauls, so hitting 75k is at times tough, especially since I want to keep my Plat with AA (60 segs). So I have to look at doing real short legs on AA so can get get the segments, then doing the longer legs on NW for the mileage. Last year, I had 110 segs on NW/CO combined, which amounted to 78k in mileage.

Should I ever shortfall the mileage on NW and they don't keep me as Plat, I'll switch to CO OP since the segments matter to them.