Unpopular opinion : AA gets the most flak because they have the most flights. They're double the size of UA. From a cancelation / delay point of view I don't think they are actually worse, but are perceived so sure to their size.
For example, yesterday saw : UA 40% delayed and 19% canceled. AA was 32% delayed and 3% canceled
Today as of now is UA 43/19 and AA 21/2
and Saturday, prior to current storm, was UA 27/4 (123 flights) vs AA 32/0 (20 flights)
Data from flightaware