1. Wells Fargo ( WFC) One to four family mortgage loans as a percentage of total assets: 28.2% The smallest of the four giant U.S. banks, Wells Fargo may be the most directly exposed to the U.S. consumer, as it has significantly smaller investment banking operations than Citigroup ( C), JPMorgan Chase ( JPM) or Bank of America, and it has a smaller international presence than those institutions. Wells Fargo has over 70 million customers, serving one in three American households, according to recent comments by CEO John Stumpf, speaking at a recent conference hosted by Barclays Capital. Stumpf said Wells Fargo has 9,000 stores in all 50 states. "We have more stores and serve more communities than any other U. S. bank," he said. Wells Fargo's first quarter results were a disappointment, according to Oppenheimer analyst Chris Kotowski, who nonetheless maintains an "outperform" on the stock. "It's the A student who got a B- on the first quiz of the semester, but there's still lots of time to raise the grade," he wrote in a recent report. >>To see these stocks in action, visit the 5 Banks Most Vulnerable to New Housing Meltdown portfolio on Stockpickr. -- Written by Dan Freed in New York.