Bank of America credit is rated Baa2, compared with A2 for JP Morgan Chase. Both of these banks have similar structures and similar product lines. Bank of America is more heavily oriented towards retail, while JP Morgan Chase has a strong investment banking business. The latter factor contributes to the superior stability of JP Morgan's business. Also contributing to the superior performance of JP Morgan is that the companies it acquired in the 2000s were much stronger than the acquisitions that Bank of America made. Merrill Lynch in particular was a difficult acquisition for Bank of America, and has set the bank's progress back. Moody's has also noted that the business models of global investment banks are inherently risky. Adverse developments, Moody's notes, "can often lead to the rapid deterioration in the creditworthiness of a given institution." The outlook for JP Morgan is also negative, though the reason cited in that case is that "government support for U.S. bank holding company creditors is becoming less certain and predictable." In other words it the view of Moody's that the too big to fail doctrine is losing political capital and the banks might actually have...

These banks are the top two in the country, with retail, investment banking and credit card businesses. However, the path that the banks took to get to this position is different in terms of the quality of assets acquired, such that the outlook for JP Morgan Chase is superior to that of Bank of America.
Works Cited:

Farrell, M. (2012). JP Morgan's trading loss: $5.8 billion. CNN. Retrieved November 21, 2012 from http://money.cnn.com/2012/07/13/investing/jpmorgan-earnings/index.htm

Son, H. (2011). BofA loses No. 1 ranking by assets to JP Morgan has Chief Moynihan retreats. Bloomberg. Retrieved November 21, 2012 from http://www.bloomberg.com/news/2011-10-18/bank-of-america-loses-no-1-ranking-by-assets-to-jpmorgan-chase.html

Moody's. (2012). JPM Q3 2012 earnings commentary. Moody's Investor Service.