Even though it doesn't seem like the words "favorite" and "bank" belong in the same sentence, there is one financial institution that's bucking the industry's trend when it comes to customer satisfaction: the United Services Automobile Association, or USAA.

According to CustomerGauge, USAA outmatched all other major banks in terms of its net promoter score, which reflects survey respondents' answers to this question: "How likely is it that you would recommend our company, product, or service to a friend or colleague?"

This may seem like an overly simple question, but it's turned out to be one of the key metrics that investors and analysts use to assess a company's prospects. "[E]vangelistic customer loyalty is clearly one of the most important drivers of growth," said Frederick Reichheld in his seminal study on the subject. "While it doesn't guarantee growth, in general profitable growth can't be achieved without it."

So how did the nation's biggest banks perform? USAA came out on top with a score of 81. The runner-up, BB&T, came in at 18, followed by PNC Financial, TD Bank, and US Bancorp, at 15, 10, and 3, respectively. Because all of these numbers are positive (above zero, that is), it means that more people promote these companies than disparage them.

More specifically, when respondents answer the net promoter score question, they do so on a scale of 0 to 10.

  • People who score a 9 or 10 are said to be "promoters."
  • People who score from 0 to 6 are considered "detractors."
  • And people who score a 7 or 8 are "passives" and are excluded from the final calculation.

The net promoter score, in turn, is calculated by subtracting the percentage of respondents that are detractors from the percentage of promoters. For example, if 60% of people are promoters, and 30% are detractors, with the remaining 10% falling into the passive category, then the score is 30. In this way, a company can score anywhere from a positive 100 to a negative 100.

It stands to reason that all five of the banks identified generally meet or exceed their customers' expectations.

Alternatively, and this likely won't come as a surprise, the nation's biggest banks all had negative net promoter scores. Citigroup was the worst with a score of negative 41. Bank of America was second worst, with a score of negative 24, followed by Wells Fargo, and JPMorgan Chase, at negative 12 and negative 1, respectively.

It doesn't take much of an imagination to appreciate why this is the case. Not only did all of these banks play leading roles in the financial crisis -- though Wells Fargo and JPMorgan Chase were somewhat unjustly lambasted because of their size and association with the more culpable too-big-to-fail banks Bank of America and Citigroup -- all of them continue to find themselves in the headlines. Over the past few years, for instance, federal legal and regulatory agencies have implicated all four of these banks in efforts to manipulate a wide range of markets, from energy markets to interest-rate markets, and seemingly everything in between.

In sum, looking at the net promoter score gives investors yet another way to gauge not only the success of companies such as USAA, but also the failures of companies such as Citigroup and Bank of America.