Gotta agree with Randy and PG - having mileage at award levels in UA and AA is a particularly nice combo to have. You've got the whole world pretty much covered.

As an example, in Sept. and Oct. of this year, we are taking a month-long trip entirely using UA and AA awards. With only one or the other, we could not have made the trip happen with the availability, stopovers, and open jaws that we needed. (One of the cities in which we have a stopover is Chicago - that certainly helps in this case.)

I am NOT a United fan by any means (haven't bought a paid ticket since the summer from hell and have no plans to do so), but you can't beat their route structure as a complement to American's. For that reason, I keep the UA account active and continue to earn partner miles there, even though I don't fly UA.