Credit card rivals MasterCard (NYSE:$MA) and Visa (NYSE:$V) released earnings on Wednesday, and both knocked the ball out of the park.

We’ll start with MasterCard.  This smaller of the two rivals enjoyed earnings growth of 25% in the first quarter and a 17% increase in worldwide purchase volumes.  Not to be outdone, Visa announced a 30% rise in earnings per share on an 11% rise in payments volume.

I admit, I’m a little partial to Visa.  The stock was my pick last year in InvestorPlace’s “10 Stocks for 2011” contest, and it crushed the competition.  (Alas, Turkcell (NYSE:$TKC), my pick for 2012, is off to a slower start—for now).

But as great as Visa’s performance has been over the past year and a half, MasterCard has been the better stock.

As a smaller, nimbler company, MasterCard’s growth has been more impressive than Visa’s in recent years, and MasterCard suffered less fallout from the Dodd-Frank Durbin Amendment fiasco that sought to limit the fees charged to merchants for debit cards.  Yet I contend that Visa remains the better long-term buy for reasons I’ll address shortly.  First, I’ll throw a bone to MasterCard bulls.

One of the provisions of the Durbin Amendment allowed merchants to choose the network that they used to process debit card transactions.  As the bigger of the two networks, Visa had far more to lose than MasterCard, and MasterCard has profiting handsomely at Visa’s expense.  Visa’s debit volume grew by only 2% for the quarter, while MasterCard’s grew by over 20%.  MasterCard will likely continue to nip at Visa’s heels for the foreseeable future in the U.S. debit market, which is the single most important segment of Visa’s business.

MasterCard and Visa have both benefitted from improving consumer sentiment in the United States and, outside of Europe, a healthier global economy.  But even if consumer spending growth is tepid in the years ahead, there is every reason to believe that both MasterCard and Visa can continue to see spectacular growth in purchase volumes (both credit and debit).

The world is going cashless.  Perhaps nothing illustrates this more than the various new iPhone credit-card-swiping apps.  Yes, next time you borrow $20 from your buddy, you can pay him back using nothing more than a credit or debit card and an iPhone.  Gotta love it.

Yet despite the seeming ubiquity of credit and debit cards, roughly 40% of all transactions are still carried out by cash and paper checks in the United States.  Remember, the United States is the most heavily penetrated of all major markets, so the percentage is much lower virtually everywhere else in the world.

This brings me to my primary reason for favoring Visa over MasterCard—Visa is far better positioned to profit from the rise of the emerging market consumer.

Visa already gets nearly half of its revenues from overseas, and most of this is from emerging markets. As incomes rise in the developing world, consumers have far more discretionary income than they used to, and they are spending a greater percentage of that with a swipe of plastic .

Alas, I would be remiss if I didn’t mention one big negative for Visa.  During the earnings release conference call, Visa announced that the U.S. Department of Justice was investigating the company for potential anti-trust violations related to debit card processing.  It’s too early to say how serious the investigation is or what Visa’s potential liability is, but the news sent the share price down sharply after hours.

At this stage, I do not see the investigation having a significant impact on Visa’s business, and I recommend using any weakness in the share price as an opportunity to accumulate more shares.

Disclosures: Visa is held by Sizemore Capital clients.