The Wall Street Journal released their metric of airline rankings that compares the major US carriers in categories such as "On-Time Performance", "Cancellations", "Complaints", "Involuntary Bumping", etc.
It's great to be part of the #4 airline and I'm hoping that while I'm here, I can help bump that up even more! Here's the 2015 and keeping the Blue side up!
On the other side of things, it's not really surprising to see United consistently near the bottom and never getting past #7 in any of the metrics used. It should also note that Major carriers don't necessarily include the performance of their regional partners into their own.