Go to the article -- it states in the article that Delta is ranked the best. The rankings are positive rankings, not negative. In other words, Delta at number 1 had the least number of complaints.
Here is an excerpt:
"Best among the big carriers: Delta Air Lines, DAL +1.45% which managed smooth operations even with lots of flights in the congested, sometimes stormy skies of the East Coast. Delta had the lowest rate of flight cancellations, according to FlightStats, a unit of Conducive Technologies. It was in the top three in all six measures of airline operations studied, and that consistency put it ahead of No. 2 Alaska Airlines."