Source: Wikimedia Commons.

There are good banks. There are great banks. And then there's U.S. Bancorp (NYSE:USB), the nation's largest regional lender by assets.

If it stands as an example for anything, it's that the business model of a traditional bank still reigns supreme over the universal model of its too-big-to-fail competitors like Bank of America (NYSE:BAC) and Citigroup (NYSE:C).

Lest there be any doubt, here are the two principal reasons U.S. Bancorp is so ridiculously successful.

1. Efficiency
In banking, as in virtually any other industry, one of the primary measures of a successful operation is efficiency -- that is, how much does it cost to produce each dollar of revenue?

The metric that's used to gauge this among banks is called the efficiency ratio, calculated by dividing operating expenses by net revenue.

The higher the number, the more it costs to produce a dollar of revenue, and the less that's left over to build book value or distribute to shareholders.

U.S. Bancorp's performance in this regard is simply unparalleled. In 2012, its efficiency ratio was 51% -- meaning that it costs only $0.51 to produce every $1 of revenue.

By comparison, the average among the 14 largest traditional banks in the United States last year was 63%, with Bank of America turning in the worst performance at 81%.

2. Return on equity
If there was only one metric that could be relied upon to determine the relative success of a bank, it would be return on equity.

Calculated by dividing a bank's earnings by its shareholder equity, this gauges how productively a bank is employing its shareholders' capital; the higher the number, the better.

With this in mind, it should come as no surprise that U.S. Bancorp handily outperforms its competitors in this measure.

Last year, its return on equity came in at a staggering 14.59%, outperforming runner-up Wells Fargo by 170 basis points. Once again, the worst performer in this regard was Bank of America, with a paltry 1.79% ROE.

If you were to look over the last decade, moreover, U.S. Bancorp's performance looks even more impressive. Its lead over Wells Fargo extends to 234 basis points, and it has nearly doubled the return of its peer group.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.