If your flying is mostly domestic you might want to consider Southwest.
Anathema, I know, to most here, but it has some advantages such as all-737s, no change fees, no cancellation fees, MDW is closer to downtown than ORD, and the Companion Pass if you have someone to serve in that capacity.
Big presence here.
United flyers are pretty hacked off right now; take a look at the longer threads in that forum.