There is no doubting their stature: MasterCard (MA) - Get Report and Visa (V) - Get Report are the biggest payment processors globally.

With both making a small percentage of every transaction that runs through their massive networks, they operate with minimal credit risk, unlike banks.

But the real question is, with Visa historically trading at a slight premium over MasterCard in terms of valuation and dividend yields on both stocks quite similar, how do investors choose?

Key metrics explain why MasterCard has the edge. 

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Visa is projected to deliver 14.61% earnings growth on an average annual basis for the next five years. This is lower than the 17.78% average annual earnings growth of the past five years.

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On the contrary, MasterCard is expected to deliver slightly higher earnings growth of 15.25%, similar to the rate clocked over the past five years.

Peers such as American Express and Discover Financial Services are projected to deliver average annual earnings growth of 7.74% and of 7.58%, respectively, over the next five years.

Meanwhile, using the price-earnings-growth ratio shows that Visa trades at a five-year expected PEG ratio of 1.93. MasterCard shares are available at a 1.73 PEG ratio, which reveals its true value.

One easy way to look at the profitability of these two behemoths is to compare their operating and profit margins.

Visa, with an operating margin of 66.58% and profit margin of 38.72% on a trailing 12-month basis seems better placed than MasterCard, which has a 52.77% operating margin and a 37.91% profit margin.

However, given that Visa has acquired Visa Europe, Visa's margins may came under pressure. 

A better way to look at profitability is to at look return ratios, both return on equity and return on assets. 

MasterCard's ROE of 63.72% and ROA of 21.35% beat Visa's ROE of 18.13% and ROA of 11.6%. For comparison's sake, American Express has an ROE of 26.14% and an ROA of 3.54%, and Discover Financial Services has an ROE of 20.33% and an ROA of 2.67%. 

MasterCard's stronger initiative of focusing on international markets gives it a surefire edge.

Visa is a much stronger American and European story, but both those regions have macro problems.

Visa faced a loss when Walmart dumped the company for its Canadian stores, but American Express, Discover Financial Services and MasterCard weren't affected. Visa has teamed up with PayPal, but volumes will take time to build in that deal.

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One negative for MasterCard is a $24.5 billion class action against the company related to cross-border transactions that were allegedly unfair.

However, at the moment, it is too early to determine potential losses for MasterCard. Visa has its own set of lawsuits filed by retailers such Home DepotKroger and Walmart.

Taking into account all the variables, MasterCard appears to be the superior investment option, compared with Visa.

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This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.