The main difference between Visa and American Express is that the latter acts as its own bank instead of relying on credit partners, what's called a "closed loop" model. Because it's also a bank, American Express has a broader overall business, with personal accounts and a robust business segment.

"As with most measures, we need to be careful using it when we compare the present to the past," Morgan Stanley's Michael Mauboussin said.

One stock in particular that I consider my favorite in Berkshire Hathaway's portfolio is Visa ( V 1.32%). Although it's not one of its top holdings, Visa has a competitive advantage and growth projections that make it a good choice to be a staple in many investors' portfolios for quite some time.