Every year, a couple of professors at Wichita State University look at the data airlines need to provide to the government about how often they screw things up and compile it into an Airline Quality Rating. This year's version came out yesterday and showed that airline quality, in the sense measured by the AQR, reached its highest level in 2011 in the 21-year history of the rating. Delving into the details of the methodology (PDF) it seems to me like their weighting of the different factors is pretty arbitrary, but the good news is that America's airlines improves on all four measures—more flights arrived on time, fewer passengers got bumped, there was less mishandled baggage, and there were fewer customer complaints.
The best-performing airline on these measures was AirTran which was also bought by Southwest Airlines (which is No. 6) and should cease to exist as an independent brand fairly soon. Hawaiin, JetBlue, Frontier, and Alaskan round out the top five. Bankrupt American (No. 10) and its affiliate American Eagle (No. 15) are both relatively low performers.