I think a lot of it comes down to where you fly. When we lived in Denver we were big UA fliers for obvious reason. When we moved to Atlanta we switched to DL but when we moved back to San Diego we had to make a choice. A lot of our flying was back to Atlanta or Charleston and DL gave us direct flights to ATL and flights that kept us out of ORD around Christmas, so we kept going with DL. I've had bad experiences with UA since I can remember, there's always something that went wrong and recently flew CO and found that CO was no better than UA. All experiences differ though, in the end I think it comes down to where you live and what routes you fly a lot to make the decision.