I've never been a fan of United Airlines and I frequently challenge their apologists. On-time Performance (OTP) is one of the many, many issues I have with United, along with product, customer service, fees, and pricing strategy.
The longest domestic delay involved a May 9 United Airlines flight from Los Angeles International Airport (LAX) to Houston Bush Intercontinental (IAH) that was diverted to Corpus Christi International Airport (CRP); the flight remained on the CRP tarmac for 222 minutes before continuing on to Houston.
I still don't believe that United's network and generous upgrade program makes up for their system-wide mediocrity. The more challengers they have on their core routes, the better.